When it ______ research into heart disease and its effects on the body, we do not have adequate substitutes for the use of animals.

We should not eat ________ junk food.

After a 3-week winter vacation, students usually _________ some weight when they return to school.

He tried to deal with the increasing burden of his work, but he finally________and had to take acomplete rest.[ ]

______ fine weather it is today!