【正确答案】 D

【答案解析】For (m -5)(m -45) to be positive, either both factors are positive or both factors are negative. For (m -5) to be negative, m must be less than 5, so m = 1, 2, 3, or 4 (4 values). For (m -45) to be positive, m must greater than 45, so m = 46, 47 100 (55 values). The answer is 59. [Note that from 46 to 100 there are 100 -46 + 1 — 55 integers, just as there are 4 -1 + 1 — 4 integers from 1 to 4 (KEY FACT O1).]