Answer:
B, D, E
Step-by-step explanation:
the sum of any 2 sides has always to be bigger than the 3rd side.
if they are equal, the triangle would be just a flat line (so, this is a special case, as some consider such a flat line an extreme triangle).
if they are smaller, the sides cannot connect to the third side, so it is not a triangle.
A. 3
this is such a special case, as 4+3 = 7
so, I think, your teacher would formally say this is not valid.
B. 9
4+9 > 7, 7+9 > 4 => valid option
C. 11
another special case, as 4+7=11.
so, not valid.
D. 5
4+5 > 7, 7+5 > 4 => valid option
E. 7
as D. yes, a valid option. it would be an isoceles triangle (2 equal sides).
F. 17
4+7<17
therefore, this is not a valid option
