Which is not a function of magnesium in the body

I am pretty sure the answer is letter C

Originally, the 500 shares were worth 25 bucks a share. If he only made $150 with 500 shares, the shares were worth $0.30 a share. So, subtract $0.30 from $25 to get $24.70. Divide 24.7 by 25 to get 0.988. Multiply this by 100 to change it into a percent. The share price decreased 98.8%.