Betty ___________ hard since last term．That's why her exam results are so good!（ ）
A．has workedB．will work
C．workedD．was working
The Lianyungang﹣Xuzhou High﹣speed Railway was open to the public this year.（ ）
A．180 kilometer longB．180 kilometers long
C．180﹣kilometer﹣longD．180﹣kilometers﹣long
What an amazing robot!It cook more than 5，000 dishes.（ ）
A．shallB．needC．mustD．can
The Communist Party of China will have its 100th birthday July 1，2021.（ ）
A．inB．atC．onD．around
Jim，you'd better not too much time on your mobile phone.（ ）
A．costB．spendC．takeD．pay
Miss Li，a humorous teacher，taught maths last term.（ ）
A．usB．ourC．oursD．ourselves