The opening cerenony is to be held in the lecture

网友回答

不选when,是因为这个空是表示地点的,而不是表示时间.
不选that,是因为如果用that,前边不能有逗号.
不选which,除非原题改成The opening cerenony is to be held in the lecture hall this afternoon,in _____ can seat 4 people.
选where,是因为这个空刚好是表示地点的.
======以下答案可供参考======
供参考答案1:
where 后面是“可以坐下四个人”，那当然要用表示地点的where了
供参考答案2:
选which 指先行词the lecture hall ，完整句子是the lecture hall can seat 4 people
供参考答案3:
whichseat有...座位,容纳...人[W]
The auditorium seats 3,000 people.
这个礼堂可坐三千人。