were two boys in the lab, _______ did theexperiment successfully.

What made Professor Liu thunder in the classroom yesterday? — A student’s interrupting his speech _____ the burst of his anger.

What does the lady have in her hands—She has ______umbrella in her right hand and_____ useful book in the other.

Mom, can I have some____________ now—Yes, it’s on the desk.

Every time ______ I go to school, I am usually riding my bike, _____ I take a bus.