Understanding big concepts and ideas will better ensure you comprehend the material
Working out: 6.25% = 4 half lives (20x4=80ma) 80ma is how old the rock is
The correct sentence is A.
All of the other sentences are grammatically incorrect.
Hope I helped!
I have not be 100% right, but I put <span>Those two old brothers had been having a pretty hot argument a couple of days before, and had ended by agreeing to decide it by a bet, which is the English way of settling everything</span>
