1. The airport was built years ago, but for some reason it could not be used then. Last year, however, it came into use.(来自新2-21课)
2. Letters will cost a little more, but they will certainly travel faster.(来自新2-22课)
我认为在第一句中，机场应该是被投入使用，所有英语应该是 was come into use 才对呀。
我认为第二句“信”为主语，应该是被传送的快，所以应该是 be traveled faster 才对呀。
请问，该怎么来理解，感谢您的解答 谢谢。