— How was _____ dinner at Mike's house? 

— It was great. Mike's mum is _____ wonderful cook. [ ]

A. a, the

B. the, a

C. the, the

D. a, an

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(2)单独都不充分，条件(1)和条件(2)联合起来也不充分．

x³+y³+3xy=1．
(1) x+y=1 (2) [*]