If the owner of a proprietary business invests his own cash into the business: 

 a. the cash is regarded as an expense because the owner spent money on the business 

b. none of the choices 

c. the cash is regarded as revenue because revenue increases when cash increases 

d. the cash is regarded as owner's equity (or capital) 

e. the cash is regarded as a liability because now the business owes this money to the owner