I always played the DOS version, and it has a bug so that after saving the game, it reverts to low difficulty

I found the game unforgiving enough to continue to be fun despite this bug.
I would say the best option is A, but arguments can be made for B.
First off, the player is stupid and executed an improper breach-- there should be a second crewman kneeling by the door to shoot emerging aliens and to cover his buddy, but thats neither here nor there.
Most likely, given the improper breach, he didn't save any time units anyway, so hes probably
hosed..
A single movement spent, even rotating, will cause the forward-facing alien to shoot you dead, and a single shot will most likely not kill the alien, so all you can hope for is to get two shots off before he responds.
A second strategy would be to shoot the distant alien, hoping either to kill the alien in front and then hitting the second alien, or, to get the second alien to return fire, killing the alien in front of you by mistake.
Unarmored troops with normal rifles though-- he probably doesn't have enough time units to prime a grenade after opening a door. Poor sap.