Answer from cs61c-ei (Jing Chen 16669246) for Question 4
The main reason for why this code would cause undefined results is due to the delays assigned at the logic gates. If there were added delays to the circuit elements, then the initial output at time = 0 is undefined because it takes a certain delay before the output takes on the new value. 

In addition, because the 10 ns delay is omitted, at time = 0 when the lines are executed, the selector would not be able to differentiate as to pick the value of a= 0 or a = 1 since they occur simultaneously. Hence, the output is undefined.