The side length has to be between 2 (=9-7) and 16 (=9+7). In both these corner cases the triangle will have collapsed to a line. So the correct answers are B,C,D and E, and F is a corner case. Theoretically I suppose you have to count F in as a valid answer.
a triangle has two sides of lengths 7 and 9.what value could the length of the third side be?