can you tell me?whose backpack is black?两句合成一句

can you tell me?whose backpack is black?两句合成一句
我知道从句应该变成陈述语序,回答这个从句的陈述句子是backpack is black所以合成can you tell me whose backpack is black.但是这个句子的答案我就不理解了can you tell me?whose backpack is that.按我的做题步骤先回答从句that backpack is 所以连成can you tell me whose that backpack is 可答案却是can you tell me whose backpack that is