The most abundant element by mass in the body of a healthy human adult are Oxygen (61.4%); Carbon (22.9%), Hydrogen (10.0 %); and Nitrogen (2.6%). The weight which a 75 kg person would gain if all 1H atoms are replaced by 2H atoms is
(a) 15 kg (b) 37.5 kg (c) 7.5 kg (d) 10 kg