Beijing is a beautiful city. And _____ foreign friends come to visit Beijing every month.[ ]

A. many thousand of

B. several thousands

C. two thousands      

D. thousands of

• 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．

方程4x²+(a-2)x+a-5=0有两个不等的负实根．
(1)a＜6； (2)a＞5．