宇航员从月球取回3千克的一块岩石，拿到地球上它的质量是 千克，它受到的重力是 牛．
3；29.4
It was not until the teacher had explained it three times _______ how to work out the problem.
A．did he understand
B．had he understood
C．that he understood
D．that he didn’t understood
Most students got _____ about the _____ news. [ ]
A. excited; excited
B. exciting; exciting
C. excited; exciting
D. exciting; excited
