如图是草食性动物的是( ),依据是:( )
A:①,具有门齿
B:②,具有犬齿
C:①,没有犬齿
D:②,具有臼齿
①氧元素____;
②地壳中含量最多的金属元素____;
③写出元素符号“O”的意义:____.
He is kind to me. He always ____ ____ ____ me with the problems in my study.