I was making my chemistry experiment_____the bell rang for break[ ]

Are you sure that youare satisfied with this job—Yes.Nothing can be better.

I don’t know when my son __________back, but when he__________back ,I’ll give you a call

With the development of modern industry, there will be_______ living space for wild animals.

The course _______ for introducing multicultural America ranks first in the list of Popularity Courses among students this term.