问题
选择题
Listen to the two girls！What language________?[ ]
A．did they speak
B．were they speaking
C．are they speaking
D．have they been speaking
答案
答案：C
搜题请搜索小程序“爱下问搜题”
Listen to the two girls！What language________?[ ]
A．did they speak
B．were they speaking
C．are they speaking
D．have they been speaking
答案：C
，在混合气体中充入一定量的18O2，足够长的时间后，18O原子 [ ]