单选题：There are many kinds of sports , _____ my favorite is swimmi..

—Why didn't you chat with that friendly foreigner just now?— I'd like to, but the trouble was ________ he said was difficult for me to understand. [ ] A. what which B. that whatC. that thatD. what that

Tomwasabouttoclosethewindow_____hisattentionwascaughtbyabird.[ ]A.whenB.if C.andD.till

He found it increasingly difficult to read,__________his eyesight wasbeginning to fall.[ ]A. though B. for C. but D. so

_______ you call me to say you're not attending my birthday party, I'll see you at it．[ ]A．WhetherB．ThoughC．UntilD．Unless

_____ you will carry out my instructions or I will offer the job to someone else. [ ]A. Either B. Unless C. Until D. Whether