C

At one point the the graph cuts x-axis. Equation of x-axis is y=0

Substituting... we can simplify the function to

(X+a)(X+b)

or essentially what is (-a,-b) ?... or what are the values of a & b?

i) a+b = -1 Insuff

ii) Graph intersects Y axis - so x=0, y=-6 .. replace in the parent equation to get value of ab = -6 .. insuff

from i) & ii) we have 2 equations... solve for a & b... Together they are suff => C.

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-Vikram