Larry saves x dollars per month. Will Larry’s total savings one year from now exceed his present savings by at least $500 ？（）(Assume that there is no interest.)
(1)In 6 months Larry’s total savings will be $900.
(2)In 3 months Larry’s total savings will exceed his present savings by $150.

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．

何谓直接致突变物和间接致突变物？