St (1):- x^2 > 9 

=> x<−3 or x>3 (Using wavy curve approach)

Given x<0

=> Then x<−3 as x>3 can be eliminated. Sufficient.

St (2):-  x^3 < –9

Let’s plug in values to check.

 At x=−3

=> x^3=−27<−9

Q-stem – Is x <-3

Answer-NO (as x = -3 and is not less than -3) but

 If x=−4

=> (x3=−64<−9) then the answer to the question stem will be YES. 

Contradictory answers (Yes/No) –Insufficient

Hence option (a)