四六级考试

【单选题】 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

网考网参考答案：B
网考网解析：
见第一段的第四句。 查看试题解析出处>>