Boolean logic

Propagation delay times $$t_(PLH)$$ and $$t_(PHL)$$, designate the delay for the state of a gate to change from low to high and high to low, respectively. For the circuit below, the delays for the gates are as follows:

If all of the inputs are initially held high, A = 1, B= 1, C= 1, the time (ns) it will take for the signal to propagate through to Output Z if Input C is changed from 1 to 0 at time t= 0 is: _______________

The Boolean function for shown in the F table below is most nearly:

A.  $$barA+barB$$
B.  $$barBbarAbarC$$
C.  $$B+barAbarC$$
D.  $$barB+barAbarC$$