android 布局

提示说error: Error parsing XML: unbound prefix
该怎么纠正，请指教<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="fill_parent"
    android:layout_height="fill_parent"
    android:orientation="horizontal" >    <TextView
        android:text="first line"
        android:layout_width="fill_parent"
        android:layout_height="wrap_content"
        ardroid:background="#ff0000"
        android:gravity="center_horizontal"
     />
     
    </LinearLayout>