把下列句子合并成一个宾语从句（每空一词）
Where did they spend the weekend? I wonder ...
I wonder ____ they ____ the weekend.

Where did they spend the weekend?为特殊疑问句，充当宾语从句时，连接词要用相应的特殊疑问词，所以第一空为where。后边要用陈述语序，将助动词did去掉，将spend变为过去式spent。变化后为I wonder where they spent the weekend.

略