Why is my Fragment being put above activity_main?

I cannot figure out why is my fragment that I call when I select an item from Navigation Drawer, being just put above the activity_main.xml (I can see activity_main's items also on the screen). I want my fragment to replace the activity_main.xml while an item is selected from the Navigation Drawer.

activity_main.xml

<android.support.v4.widget.DrawerLayout
    xmlns:android="http://ift.tt/nIICcg"
    xmlns:tools="http://ift.tt/LrGmb4"
    android:id="@+id/drawer_layout"
    android:layout_width="match_parent"
    android:layout_height="match_parent">

<FrameLayout
    android:id="@+id/content_frame"
    android:layout_height="match_parent"
    android:paddingLeft="@dimen/activity_horizontal_margin"
    android:layout_width="match_parent"
    android:paddingRight="@dimen/activity_horizontal_margin"
    android:paddingTop="@dimen/activity_vertical_margin"
    android:paddingBottom="@dimen/activity_vertical_margin" >
    <!-- The main content view -->

    <TextView
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:textAppearance="?android:attr/textAppearanceMedium"
        android:text="Location:"
        android:layout_marginTop="10dp"
        android:id="@+id/tv_disploc"
        />

    <TextView
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:textAppearance="?android:attr/textAppearanceMedium"
        android:text="Temperature:"
        android:id="@+id/tv_disptemp"
        android:layout_below="@+id/tv_disploc"
        android:layout_marginTop="44dp" />


    <Button
        style="?android:attr/buttonStyleSmall"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="Search"
        android:onClick="ButtonClick"
        android:id="@+id/btn_search"
        android:layout_below="@+id/et_inloc"
        android:layout_centerHorizontal="true"
        android:layout_marginTop="37dp"
        android:layout_gravity="center" />

    <EditText
        android:layout_width="174dp"
        android:layout_height="wrap_content"
        android:id="@+id/et_inloc"
        android:layout_centerVertical="true"
        android:layout_toRightOf="@+id/tv_dispsearch"
        android:layout_gravity="center" />

    <TextView
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:textAppearance="?android:attr/textAppearanceLarge"
        android:text="Search:"
        android:id="@+id/tv_dispsearch"
        android:layout_centerVertical="true"
        android:layout_gravity="left|center_vertical" />

    <EditText
        android:layout_width="126dp"
        android:layout_height="wrap_content"
        android:id="@+id/et_outtemp"
        android:layout_below="@+id/et_outloc"
        android:layout_toRightOf="@+id/tv_disptemp"
        android:layout_marginTop="30dp"
        android:layout_marginLeft="30dp"
        android:clickable="false"
        android:cursorVisible="false"
        android:focusable="false"
        android:focusableInTouchMode="false"

        android:layout_gravity="center_horizontal|top" />

    <EditText
        android:layout_width="135dp"
        android:layout_height="wrap_content"
        android:id="@+id/et_outloc"
        android:layout_toRightOf="@+id/tv_disploc"
        android:layout_marginLeft="30dp"
        android:clickable="false"
        android:cursorVisible="false"
        android:focusable="false"
        android:focusableInTouchMode="false"
        android:layout_gravity="center_horizontal|top" />
</FrameLayout>

    <!-- The navigation drawer -->
    <ListView android:id="@+id/left_drawer"
        android:layout_width="240dp"
        android:layout_height="match_parent"
        android:layout_gravity="start"
        android:choiceMode="singleChoice"
        android:divider="@android:color/transparent"
        android:dividerHeight="0dp"
        android:background="#111"/>
</android.support.v4.widget.DrawerLayout>

fragment_option.xml

<LinearLayout
    android:layout_height="fill_parent"
    xmlns:android="http://ift.tt/nIICcg"
    android:layout_width="fill_parent"
    android:id="@+id/fragment_option"
    android:orientation="vertical"
    android:fitsSystemWindows="true"
    android:minWidth="1000dp"
    android:minHeight="1000dp">
    android:weightSum="1">



    <TextView
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:textAppearance="?android:attr/textAppearanceLarge"
        android:text="Select your Default Location"
        android:layout_marginTop="100dp"
        android:layout_gravity="center_horizontal"
        android:id="@+id/textView" />

    <Spinner
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:id="@+id/spinner_locations"
        android:layout_gravity="center_horizontal" />
</LinearLayout>

I want to open a Spinner when an item is clicked from Navigation Drawer.

Any ideas?