He tried his best to solve the problem, ________ difficult it was．

Finally, the thief handed everything ____ he had stolen to the police.

The girl was not very happy,so she had to give us a _____ smile.[ ]

I can never forget the days we spent together in the summer camp.—Well, especially the day it suddenly began to rain in the middle of the night.

How long do you think it is _______ he took up the job?—Half a year at least[ ]