1) a is the level of stress at which performance is minimal.

2) a is the level of peak performance.

3) a is the level of stress at which performance is maximal.

4) a is the level of stress at which performance is 1/2 of maximal performance.

**Solution: Choice 3 is correct.**

The given function represents a parabola in vertex form.

Since, there is a negative sign in front of the squared term, the parabola will face downwards.

Also, the parabola will have vertex (a,b) with vertex describing the maximum for the function.

Therefore, the performance will be maximum for s=a with P(a) = b.

Therefore, “a” is the level of stress for which performance is maximum “b”.