这样子修改一下才对哦：
they haven't decided whether to go to beijing or not.
他们还没决定好要不要去北京.
祝好!
不懂建议重新提问,they haven't decided whether togo to beijing or not.they haven't decided on whether togo to beijing or not.有区别吗？？不用onon 后面加名词，这里不合适。