—Did you find the missing couple in the mountain yesterday?

—No,but we _____ to get in touch with them ever since.[ ]

A. have tried  

B. have been trying

C. had tried  

D. had been trying

一块白色玉牌，表面有美丽的龙形花纹，密度2.65g/cm³，具隐晶质结构，它是（）。

A.合成软玉

B.软玉

C.玻璃

D.石英岩质玉