Which of the following could be the lengths of three sides of a triangle?

A) 3, 4, 5

B) 2, 5, 8

C) 2, 12, 15

D) 3, 3, 7

For three numbers to represent lengths of the sides of a triangle, the sum of each pair must be greater than the remaining side.

A)

3 + 4 = 7

3 + 5 = 8

5 + 4 = 9

B)

2 + 5 = 7

2 + 8 = 10

5 + 8 = 13

C)

2 + 12 = 14

2 + 15 = 17

15 + 12 = 27

D)

3 + 3 = 6

3 + 7 = 10

3 + 7 = 10

In all these, only A have the sum of the numbers greater than the numbers itself. So the answer is A.