A certain alloy contains only lead, copper, and tin. How many pounds of tin are contained in 56 pounds of the alloy ?()
(1)By weight the alloy is lead and copper.
(2)By weight the alloy contains 6 parts lead and 5 parts copper
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.