how is uranlum-235 enriched?

Uranium isotope is a widely used fuel source. It is enriched artificially up to 3-5% from its natural state.  

It is a commercial process where the uranium oxide is done some conversion with chemical processing to form the uranium hexafluoride (UF6), to make it useable for the enrichment facilities.

This processing of the uranium from 0.7% to 5% enrichment by isotope separation is used as a nuclear fuel which is very useful for the commercial purpose.

the answer to your question is,

d. when a child was born.

-mabel < 3

i believe the answer is: returns on investments, no wages

people who belong in upper class society would most likely get there by obtaining multiple source of income, which a certain percentage of ownership for businesses. since most of them are job creator, they would most likely get their money from profit, not wages.