1. that...travels My teacher told me后接that引导的宾语从句,在表示真理时时态始终用一般现在时所以用travels
2.if/whether 表示是否
在以下情况下只能用whether
接不定式 如:I'm not sure whether to go.
介词之后 如:It depends on whether the letter arrives in time.
句型whether or not
引导主语从句 如:Whether they win or lose is all the same to me.