android中 MAIN.XML布局有关问题

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout 
    xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:paddingBottom="@dimen/activity_vertical_margin"
    android:paddingLeft="@dimen/activity_horizontal_margin"
    android:paddingRight="@dimen/activity_horizontal_margin"
    android:paddingTop="@dimen/activity_vertical_margin"
    tools:context=".MainActivity">

    <TextView
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:text="@string/main_title" />
    
    <Button
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:text="@string/continue_label" />
    <Button
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:text="@string/newGame_label" />
    
    <Button
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:text="@string/about_label"  />

    <Button
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:text="@string/exit_label"  />
</LinearLayout>

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout 
    xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:orientation="vertical"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:paddingBottom="@dimen/activity_vertical_margin"
    android:paddingLeft="@dimen/activity_horizontal_margin"
    android:paddingRight="@dimen/activity_horizontal_margin"
    android:paddingTop="@dimen/activity_vertical_margin"
    tools:context=".MainActivity">

    <TextView
        android:layout_width="match_parent"