答案：B

解析：

The sum of the lengths of any two sides of a triangle must be greater than the length of the third side. Four of the answer choices can be eliminated because each set of three numbers can be the lengths of three sides of a triangle. For example, in the third choice (1,75,75), the sum of any two numbers is greater than the third number. However, the second choice (1,2,4) cannot be the lengths of the sides of a triangle, since 1 + 2 is not greater than 4. This choice is the correct answer, since the question asked which set of numbers could NOT be lengths of the sides of a triangle.