In a triangle ,
sum of two sides>third side
let us check for each option one by one
Option A:
{4,7,9}
4+7>9, 11>9 (true)
4+9>7, 13>7 (true)
9+7>4, 16>4 (true)
so it represents sides of triangle
Option B:
{9,10,11}
9+10>11, 19>11 (true)
10+11>9, 21>9 (true)
9+11 >10, 20>10 (true)
so it represents sides of triangle
Option C:
{4,8,12}
4+8>12, 12 >12 ( false)
so this does not represent sides of triangle
Answer is option C {4,8,12}