Before entering the classroom, Professor Lucas heard_________.

A. in that B. that

C. which D. in which

A. are working B. have been working

C. have been worked D. work

A. Observation B. Observatory

C. Observed D. Observing

A. More medicine taken B.When I take more medicine

C. The more medicine I take D.Taking more of the medicine

A. once a four years B. four years a time

C. for four years D. every four years

A. can we do B. to be done

C. shall we do D. to doing

A. No wonder B. No way

C. No problem D. No doubt

A. would have B. would have had

C. had had D. should have

A. love

B. effect

C. tie

D. relationship

A. It's easier to buy a baby dog under three months old.

B. They are less likely to be shy with human beings.

C. They are less likely to run away.

D. It's esier for them to form a relationship with their masters.