The students _______ busily when Miss Brown went to get a book she _______ in the office

_______ difficulty we meet with, we must finish it on time, because the opportunity is_______ valuable．

____Mary____ Lucy has joined the art club because they have no time.

he was 12, Einstein had learned advanced mathematics by himself.

(2013·高考重庆卷)John invited about 40 people to his wedding，most of________are family members.