下列情境中，售货员的回答最得体的一项是（ ）某顾客到商场买拎包，她看不出自己选中的拎包是否用真皮制成，她听说过一种检验是否真皮的做法，就是用指甲划包包，真皮是划不破的。她向售货员提出自己要求。面对这过分的要求，售货员微笑地说：“ ”

Mr. Zhang, our math teacher, is strict with students and serious in teaching work, so he ____.

do you often play with at weekends — My best friend, Mary.

The problem is _____ difficult for me _____ solve

We do morning exercise every day, from which we ______ a lot.