C. The Triangle Inequality Theorem States that any two sides of a triangle must be greater than the third side. It cannot be A because 35+40= 75, which is not greater than 75. It cannot be B because 40+30= 70, which is not greater than 75. It cannot be D because 35+40= 75, which is not greater than 80. It is C because 40+30= 70, which is greater than 65.
