can you tell me?whose backpack is that?合并成一句我的答案can you tell

can you tell me?whose backpack is that?合并成一句我的答案can you tell me whose that backpack is
我做的答案是错的,我认为宾语从句的从句应该是陈述句子才用的that backpack is 正确答案是can you tell me whose backpack that is请大家帮我分析错误的原因我及时改正