敞开装设在金属框架上，保护和操作方案较多，装设地点灵活的低压断路器为（）。

A.SF6低压断路器 

B.万能式低压断路器 

C.塑壳式低压断路器 

D.固定式低压断路器

Company R’s annual profit has increased by a constant amount each calendar year since 1985. What was Company R’s annual profit in 1991 ？（）
(1)In 1985 Company R’s annual profit was $212.000; in 1989 Company R’s annual profit was $242,000.
(2)Company R’s annual profit has increased by $7,500 each year since 1985.

A．条件(1)充分，但条件(2)不充分．

B．条件(2)充分，但条件(1)不充分．

C．条件(1)和(2)单独都不充分，但条件(1)和条件(2)联合起来充分．

D．条件(1)充分，条件(2)也充分．

E．条件(1)和条件(2)单独都不充分，条件(1)和条件(2)联合起来也不充分．