解一道有英语的奥数题：The sum of n different positive integers is less

解一道有英语的奥数题：The sum of n different positive integers is less than 50.
The sum of n different positive integers is less than 50.The greatest possble value of n is( )
A.10 B.7 C.8 D.9
其中positive integers 是正整数的意思.
求奥数和英语都特厉害的大师相救啊!
回答时顺便列一下式子啊！