Questions 11 to 18 are based on the conversation you have just heard.

A．There were laws that protected the rights of slaves.
B．Nobody in the U. S. disagreed with slavery before 1800.
C．There was progress in the opposition to slavery.
D．The end of the Civil War enabled blacks to enjoy equality

A．Nowadays, scientists pictured the circulation of ocean’s water mass as consisting of large slow-moving currents.
B．Before 1965 ,the concept of scientists produced only a rough approximation of the true circulation.
C．Researchers began to do research on the developed techniques and equipment.
D．These instruments disclosed an expected level of variability in the deep ocean.