My friends went to summer camp _______ vacation. [ ]
A. at
B. on
C. in
D. for
答案:B
嵌体箱状洞形轴壁向
面外展的角度不应超过()
A.5°
B.30°
C.45°
D.90°
E.135°
羧酸型树脂H型和Na型的交换速度有很大差别,这是由于交换基团不同型态,膨胀率变化很大所致。()