This old building was built in _____ .

I won’t tell the student the answer to the math problem until heon it for more than an hour

There was a big dog ______ in front of Mr. Hill’shouse, so David didn’t dare to go near it.

Mr Black is a careful and experienced worker, so he is often to finish some challenging tasks. [ ]

．_______we couldn’t understand was _______ more and more students went abroad aftergraduation.