Teacher's Helper is a small company that has a subcontract to produce instructional materials for disabled children in public school districts. The owner rents several small rooms in an office building in the suburbs for $$600$ a month and has leased computer equipment that costs $$480$ a month. $($The small rooms and computer equipment are under contract and therefore cannot be changed in the short run.$)$

On average, people in $1950$ spent

a$.$ the same percentage of their disposable income on food as people did in $1960.$

b$.$ a smaller percentage of their disposable income on food than people did in $1970.$

c$.$ a greater percentage of their disposable income on food than people did in $2014.$

d$.$ the same percentage of their disposable income on food as people did in $2000$