Students here often do physics experiments _____small groups．（ ）
A．byB．inC．forD．at
To prepare for _____trip to LA， Betty is making _____list of things to take along．（ ）
A．the； theB．不填； aC．the； aD．a； 不填
There is so much noise in the next room．I wonder__________________．（ ）
A．what are they doingB．what were they doing
C．what they are doingD．what they were doing
Smile to the world， ________the world will smile back to you．（ ）
A．andB．orC．butD．if
The window broke into pieces shortly after the plane _______．（ ）
A．got offB．took upC．got upD．took off