驼背现象是（）较差所至。
A、腹肌力量
B、背肌力量
C、胸肌力量
参考答案：A
It wasn't until nearly a month later _______ I received the manager's reply. [ ]
A. since
B. when
C. as
D. that
对于实数λ≠0，非空向量零向量，下列各式正确的是()．
A.A
B.B
C.C
D.D
零向量
，下列各式正确的是()．