30.at one time曾经;一度
At one time this factory employed 400 people.这家工厂曾经雇用过400名员工。
31.at the same time
(simultaneously)同时
I can't cook a big dinner and look after the kids at the same time!我无法在准备一顿大餐的同时还照看孩子!
(nevertheless)但是
I was afraid of her, but at the same time I really liked her.我很怕她, 但我也真的很喜欢她。