Jack, what about the lecture— It is the most inspiring lecture that I _________ since I came to this university.

She learned how to ride a bike _________ at the age of 6.

When did you return to Nanjing last Friday?—It was not until midnight _______ it was snowing heavily.[ ]

I actually prefer to stay up _______ at night, but not _______ I’m working the next day

1I_______ like science but I think it is very useful.