半月板损伤的主要临床表现有（）。
A.膝关节疼痛
B.膝部弹响
C.膝部交锁征
D.股四头肌萎缩
E.挺髌试验阳性
参考答案：A, B, C, D
若a≥0时，则|a|=______；若a＜0时，则|a|=______．
It was several minutes _______ we realized what was happening~our dog was trapped in a newly-dug tunnel.
A．since
B．before
C．until
D．while
