单选题 If S is the sum of the first n positive integers, what is the value of n ?(1) S<20(2) S2 >220

A、 Statement (1) ALONE is sufficient, but statement (2) alone is not sufficient.
B、 Statement (2) ALONE is sufficient, but statement (1) alone is not sufficient.
C、 BOTH statements TOGETHER are sufficient, but NEITHER statement ALONE is sufficient.
D、 EACH statement ALONE is sufficient.
E、 Statements (1) and (2) TOGETHER are NOT sufficient.

【正确答案】 C

【答案解析】(1) Given that S < 20, n could be 5 since

= 15 < 20. However, n could also be 4 since

；NOT sufficient.(2) Given that S2 > 220, n could be 5 since

= 15 and 152 = 225 > 220.However, n could also be 6 since

= 21 and 212 = 441 > 220;NOT sufficient.Given (1) and (2) together, it is clear from the following table that n = 5.