Larger tonnage refrigerant units use which kinds of chillers?

Larger tonnage refrigerant units use which kinds of chillers?
 
  A) reciprocating and scroll compressor chillers B) scroll and centrifugal compressor chillers
  C) centrifugal and screw compressor chillers D) reciprocating and screw compressor chillers

 Q. 2

To avoid system breakdown due to the failure of components that have a predictable service life, it is wise to:
 
  A) Schedule parts replacements for wear items near the end of their service life.
  B) Install another backup system which can be quickly brought online.
  C) Not purchase any equipment that has parts that can wear out.
  D) Always use pulleys that have two belts.