Over the past 100 years the amount of fossil fuel consumption has

Over the past 100 years the amount of fossil fuel consumption hasdecreased

The correct answers are B & C. Silicon-32 is the parent isotope, which decays into phosphorus-32 (daughter isotope). The silicon-32 amount is halved every 170 years, so we can use this to determine how old the rock is. The amount of phosphorus-32 increases over time, but it is not equal to the amount of silicon-32.