题干
—Please go and say hello to your aunt．She’s in the living room now．
—She has arrived! But when ______ she ______?
—She has arrived! But when ______ she ______?
A：will; arrive
B：did; arrive
C：had; arrived
D：has; arrived
答案(点此获取答案解析）
B
2SO3, 在混合气体中充入一定量的18O2, 足够长的时间后, 18O原子（ ）
