单选题   Although most dreams apparently happen ______, dream activity may be provoked by external influences.
 
【正确答案】 C
【答案解析】 homogeneously同样地;instantaneously即刻,突如其来地;spontaneously自发地,不由自主地;simultaneously同时地。根据句意,大多数梦境都是自然产生的,故选C。