When he was doing the software development project, he ___________ many problems that he had to solve on his own.
Many children seldom communicate with adults, ________ it difficult for their parents to know what they are thinking about.
The headmaster demanded all the teachers ______ in the office.
—How was that? —I was chatting on line ______ the power went out.
In order not to be disturbed, I spent three hours _______ in my study.
—What shall I do, go back home or stay here, since it’s so late? —______. The bus is leaving.