I didn’t quite follow him because he explained the theory _____that is too abstract for me

t ______ research intoheart disease and its effects on the body, we do not have adequate substitutesfor the use of animals.

39.It’s demanded that we____________there on foot.40.

Is there________ book by Mo Yan —Yes. It’s on______ bookshelf over there.

David is very __________ and he can always make the people aroundhim happy.