Answer:
c
Step-by-step explanation:
Two sum of any two side lengths of a triangle will always be greater than the length of the remaining side
a doesn't work because 8+12=20 and 20 is not greater than 20
b doesn't work because 4+5=9 and 9<10
d doesn't work because 6+6=12 and 12 is not greater than 12
c is the only option where you can take any two sides, add them, and the sum will be greater than the remaining side.
For example, for c,
6+8=14, and 14>10
8+10=18, and 18>6
10+6=16, and 16>8
