高三英语语法题：特殊句式.请求详解!

— You should have thanked the hostess before leaving. — I meant __B___. But I couldn't find her when I was leaving.                             A. to do B. toC. doing D. doing so（为嘛不选A?）

Lovely day, isn't it? Yes,__B_____.    A.you are right B.isn't it?  C.sure D.is it?(这题答案真的没给错吗?)

———I had a few problems to deal with.A hardly have I arrive when       B hardly did i arrive than     C hardly had i arrived when        D hardly had i arrived than (能解释一下其他选项的意思以及用法吗)

高三狗请求高人指点.