Passage Three
Questions 33 to 35 are based on the passage you have just beard.

A．To explain the effects of turbidity currents.
B．To explain how winds cause turbidity currents,
C．To remind the student about the next assignment.
D．To remind the student where ocean sediments originate.

A．He usually talks quietly.
B．He usually assigns homework.
C．He didn’t teach class today.
D．He noticed that the students didn’t do their homework.