Upstairs C:
Anything that has a longer barrel than an MP5k can easily hit guys aiming over the balustrade. Usually.
Or you could just cloak your way up the enemies' balcony and horribly melee anyone up there.
Being upstairs has some advantages too. Sometimes I M200-derp up there, shooting whatever comes through the right corridor. Don't like the left side as much, because on the far right, the enemy has another entrace to C, and hence another angle to shoot you.
Instead, you could just bring your biggest and baddest full auto belt fed heavy Maschinengewehr, like an OP41 or a PKM and brrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrt the other guys.
Concerning point B (yes I just looked that up) you can obviously attack behind the cars. Or you could climb up the truck (using the trailer as cover), or just sit behind one of the tires and shoot under the trailer. Also I think you can cover at the walls on the right (on the far side of the point), but that's fairly risky, because you're quite at the front.
Defending B is a bit difficult, I would suggest not letting the enemy get to B by camping them out somewhere between C and B. I'm going to state the obvious: you can take cover behind the cars, and also behind the tires of the big truck (but, it being obvious, it's where the bad guys expect you to be.
When defending, a quite effective move is to move past the point on the (defenders') right, get up on the low balcony thingy at that café or whatever that is, and then take the enemies out from their "behind left side".