when ------to biology,I know nothing.A I come B It comes

when ------to biology,I know nothing.A I come B It comes it在这里到底是什么语法成分?指的是什么呢?When it comes to German,I know nothing I want to know you will come at 8:00 tomorrow A.that B.when i dont know when he will come.when he comes,i will call you. I don't know if he__ A:comes,B:will come I’m afraid it will be two months A.when I come back B.when I 英语翻译When it comes to the people I care about,I learned a lon A;Do you know anything about it B；No,I know nothing…… he tol •it在这里到底是什么语法成分?指的是什么呢?When it comes to German,I know it's a (m ) to me because i know nothing about it I should take caution when it comes to 翻译When it comes to friends,I desire those