First we need to find if the coefficients are negative or positive. The function:
Is always positive which means that its graph must be over the x axis. If this function is multiplied by a positive coefficient then the graph remains over the x axis. On the other hand, if it's multiplied by a negative number then the graph is now under the x axis. A and B graph are over the x axis so they are positive whereas C and D graphs are under the x axis and they are negative and that's the answer for a.
Then we must find the coefficient with the greatest value. Since a positive number is greater than any negative number we can discard C and D. Now we have two options, A and B which we know are different numbers since their graph are different. Both are V shaped but graph B is sharper than graph C. This means that B is greater than C. Then, the answer to part b is coefficient B.
In part c we must choose the coefficient that is closest to 0. Using the same argument as before, the sharper the V shaped graph is the greatest absolute value its coefficient has. This means that the least sharp graph is that of the coefficient that is closer to 0. Looking at the four graphs you can see that the least sharp V is that of coefficient A. Then, the answer to part c is coefficient A.