LHS = left hand side

RHS = Right hand side

A. (7 + 8) + 9 = 7 + (8 + 9)

Is true due to associative property of addition.

B. (7 × 8) × 9 = 7 × (8 × 9)

Is true due to associative property of multiplication.

C. LHS = 7 + 8 × 9

= 7 + 72

= 79

RHS = (7+8) × (7+9)

= 15× 16 = 240

As LHS ≠ RHS,

It is incorrect.

D. 7 × (8 + 9) = (7 × 8) + (7 × 9)

It is true due to distributive property of addition over multiplication.