单选题 Although there are many predictions about the future, no one knows for sure ______ the world would be like in 50 years.
【正确答案】 D
【答案解析】本题测试宾语从句的引导词。谓语动词knows后面的宾语从句中缺少一个引导词，根据句意和结构，该引导词应在从句中做like的宾语，表示什么样，故只能用what。