While deploying a new switch, you accidentally connect ports 3/12 and 3/18 together, creating a
loop. STP detected it and placed port 3/18 in blocking mode. Why did STP not place port 3/12 in
blocking mode instead?

A.
Port 3/12 was already up and forwarding before the loop was created.

B.
Port priority is based on lowest priority and lowest port number.

C.
You connected the wire on port 3/18 last.

D.
None of the above, it is purely random.

Explanation:
Spanning-tree select the port, by first calculating the cost (which depends on the bandwidth) then

the port priority which is based on the lowest priority (in case configured) and the lowest port
number.