问题
I wonder ________ as the ads has promised.
A:does the air-cleaner really work
B:the air -cleaner really works
C:that the air-cleaner really works
D:if the air-cleaner really works;
B:the air -cleaner really works
C:that the air-cleaner really works
D:if the air-cleaner really works;
正确答案是：
