If there's anything you need while you're in town, just let me know.
你在镇上有什么需要,就告诉我吧。
I will have done it by the time you come back.
在你回来之前,我会做完它。[将来完成时,表示将完成…,会做完…]
A burst of activity associated with the laying of submarine cables soon confirmed the Challenger's observation that many parts of the ocean were two to three miles deep,