6. In 1948, three American scientists invented ______ transistor, which is ______ small electronic device to control an electric current.

A. the; a                B. a; a                          C. the; the                    D. a; the

7. I would appreciate ______, to be frank, if goods could be delivered as soon as possible.

A. you               B. this                      C. myself                  D. it

8. —I didn’t know you were good friends.

—You     . I have known her since she moved here. You were studying abroad then.

A. may have     B. couldn’t have C. needn’t have      D. must have