题目

Tom got up late so he had to run all the way to the school, and got there quite out of________. A．work                              B．breath C．sight                             D．mind 答案：B 题意：汤姆起床晚了，不得不一路跑着去上学，到学校时他已上气不接下气。out of breath“上气不接下气”，符合题意。out of work“失业”；out of sight“看不见”；out of mind“忘却；不想”。（2003•贵阳）如图，已知AB为⊙O的直径，AC为弦，OD∥BC，交AC于D，BC=4cm．（1）求证：AC⊥OD；（2）求OD的长；（3）若2sinA-1=0，求⊙O的直径．