General Motors, one of the world's largest auto manufacturers, is expanding its ________ in this country.

Becareful,_______you'llfalldown.

When he suddenly ________ up the subject of genetic engineering, there was an embarrassedsilence.

I don't know how we can make ________ on the timetable for any more courses.

Human behavior is mostly a product of learning ________ the behavior of animals dependsmainly on instinct.