在弱、强型树脂联合应用中，弱型树脂和强型树脂在系统运行中各起什么主要作用？

He was puzzled by this phenomenon. He began to try every approach _________ the best way of working it out.

A．known to find

B．knowing to find

C．known finding

D．knowing finding

用托盘天平称1粒米的质量，较好的办法是[ ]

A．认真仔细地直接测量一粒米的质量

B．先称一粒米与一块木块的共同质量，再测木块质量，然后计算求得

C．多次测量取平均值

D．先称100粒米的质量，然后计算求得

______ of the information about the show ______ downloaded from the Internet. [     ]

A. Three-fourths; were

B. Three-fourths; was

C. Third-fourths; were

D. Third-fourths; was

103型分配阀是一种元滑阀结构的阀。

拱形支架更换一侧柱腿时的注意事项是什么？