Unable to resolve target 'android-16'

Just now when I imported the "android-support-v7-appcompat" to ADT,the console pointed out "Unable to resolve target 'android-16'".

I double clicked the project.properties file, change the target = android-17 attribute to target = android-19, android api level 19 is my ADT's latest compile environment (you can find it in File-New Android Application tag).Problem solved.