单项选择题
From the passage we know that joints and muscles perform best when（）
A．they are twisted and stretched B．they are in their normal positions C．they are tested with a human "guinea pig" D．they are tested with electronic instruments
单项选择题 Why is it useful to carry enough 25-cent coins with you （）
单项选择题 When you post a letter, you must buy ______ .
单项选择题 We may conclude that （）
