Thinking that the students were having an evening class, the teacher left the classroom, _____.

In my opinion, she is too young to take care of the pet dog ______.

Cloning plants is straightforward while cloning animals is _____________ more complicated.

 —Do you regret paying ten dollars for that book?—No, I would gladly have paid ________. 

He trained hard in puzzle-guessing, a sort of children’s game, all year, _____ still failed to reach his best form in all the tests given to both adults and children.