When will they come here ? I really don't know .(合并为一句)I really don't know when __ __ come here .

问题描述:

When will they come here ? I really don't know .(合并为一句)
I really don't know when __ __ come here .

they will
宾语从句:连接词+ 陈述句( 主语+谓语)