Which of the following is an example of an equation with exactly one solution?

A: 3x + 4 = 3x + 4
B: 4x + 3 = 4x + 3
C: 3x + 4 = 4x + 3
D: 3x + 4 = 3x + 3

A: 3x + 4 = 3x + 4