1 . With all his attention_______(concentrate) on the painting, he didn’t notice me come in. (所给词的适当形式填空)

2 . During class time, students need to c ______ on their teachers' speeches. （根据首字母单词拼写）

3 . If you ____________   on (专注于) English, you’ll have a good command of it sooner or later.. (根据汉语提示填空)

4 . If you c_________(集中)your effort on learning English, you will master the language.(根据汉语提示单词拼写)