Answer:
Option D is correct.
Explanation:
We use the following result:
If sum of two sides of a triangle is greater than third side then Triangle is possible with those sides.
Option A).
a = 21 , b = 7 , c = 7
a + b = 21 + 7 = 28 > c
b + c = 7 + 7 = 14 < a
So, These length cannot be lengths of the sides of the triangle.
Option B).
a = 20 , b = 6 , c = 8
a + b = 20 + 6 = 26 > c
b + c = 6 + 8 = 14 < a
So, These length cannot be lengths of the sides of the triangle.
Option C).
a = 15 , b = 5 , c = 20
a + b = 15 + 5 = 20 = c
So, These length cannot be lengths of the sides of the triangle.
Option D).
a = 9 , b = 14 , c = 22
a + b = 9 + 14 = 23 > c
b + c = 14 + 22 = 36 > a
a + c = 9 + 22 = 31 > b
So, These length can be lengths of the sides of the triangle.
Therefore, Option D is correct.