She didn’t know__________she could express her ideas clearly when she was invited to speak at the meeting.

I was doing my homework _______ mother was cooking.

—My sports shoes are nicer than yours?—Yes, but mine are _________ yours.

—What’s the matter with you? You look so worried.-- I don’t know ___________ the problem.

—Every day, my mother tries to spare some time to chat with me,        she  is very tired after a whole day’s hard work.—You are lucky to have such a great mum!