The group’s research has done much to our knowledge of the HIV virus．
| A．advance | B．pull | C．rush | D．adopt |
Happiness and success often come to thoseare good at recognizing their own strengths.
| A． | whom | B． | who | C． | what | D． | which |
I ________ to visit you later that day, but I had to phone and cancel.
| A．come | B．came | C．am coming | D．was coming |
Ifto look after luggage for someone else, inform the police at once.
| A． | asked | B． | to ask | C． | asking | D． | having asked |
He wrote a letter ______ he explains what had happened in the accident.
| A．what | B．which | C．where | D．how |
Animals are obviously ______ lower form of life than _______ man.
| A．a ; / | B．the ; the | C．a ; the | D．/ ; / |