How many companies in the S&P 500 list have a Market Cap of at least $20Bn AND Revenue of at least $15Bn?

explanation:

a gas is not used in hydraulic machines as the fluid because gas is easily compressible and so if a gas is used, the energy would mostly go into compressing a gas. therefore a liquid is used in hydraulic machines as the fluid.

answer'; i believe the correct answer is (15,000) workers a year are treated for injuries caused by jacks, lifts or jack stands;

b. take periodic breaks and alternate between tasks.  

will increase work efficiency, and avoid health issues.

answerobservation;