What is generally used as a preservative for preserving blood?

Acid-citrate-dextrose anticoagulant at 4C for period is to three weeks.

I’m going to guess these are the choices: a) recreational skiing developed in the mid-19th century b) it was originally invented as a way of getting from place to place in snowy regions c) downhill skiing is currently the only common form of the sport d) it mostly evolved from snowshoeing- if that’s the cases then the answer would be c) downhill skiing is currently the only common form of the sport