单选题 How many positive integers n have the property that both 3n and n/3 are 4-digit integers?

A、 111
B、 112
C、 333
D、 334
E、 1，134

【正确答案】 B

【答案解析】If n is an integer, then 3n is always an integer. Also, 3n will be a 4-digit integer only when 1,000 ≤ 3n ≤ 9,999.Therefore, n is an integer such that