You probably have all seen it, you are ordered to get a flag, only to find (often just 1 pack) C4 on the flag.
Some will just try to get the flag and die but there are ways to avoid this.

1: C4 explosions are affected by collision, this means if you can hide behind a wall your chances are much higher. Also, if C4 is put at the base of the flag, put yourself on the opposite side. Every little bit helps!

2: C4 has a range of 10m (10m is the 10m you see with the 3D alt on, like you see when you see a friendly mine), at 10 and 9m, you will get hurt, but you will live, so if you see a C4 strapped on a flag, look up at the flag and see if you can get 8m or more away from the flag while still capping it. If there are multiple C4, try to find where they all are and see if you can find a safety gap.

3: C4 can be detonated by another pack of C4. If you have a Spec Ops on your squad, or you are Spec Ops, just place a C4 pack over the enemy C4, walk away and detonate it, it should go off with it.

4: Often, the C4 won't detonate until the moment the flag goes grey/neutral, so what you can do, is try to stay as far away from the flag as possible (and the C4 of course) while you are still in the capping range/radius. The second the flag goes neutral, run away behind a corner or at least a safe distance from the C4. Then wait something like 5 seconds. The guy who put the C4 there will see the flag is neutral, and will detonate the C4 and then you can get the flag afterwards.

5: If you see a lot of C4 packs (all over the place) then there is a chance a Spec Ops is actively gaurding the flag, (which means he is watching it). If you think this is the case, stay away from the C4 and look around and try to spot the enemy Spec Ops. Also try roofs. When you find him, kill him and you can do 2 things, you can either then go straight back to the flag. (this might mean that another enemy will pick up the Spec Ops kit and blow the C4). Or, you can pick up the Spec Ops kit and detonate the C4 yourself so you are sure its safe. (Make sure you don't blow any friendlies!).

6: You can ofcourse at any time just try your luck and hope the C4 wont blow until you get the flag, 9 out of 10 it won't blow until the flag goes neutral.