$4.\_\_\_\_\_\_\_.$ You called the Boston Consulting Group $($BCG$),$ and

they have provided you with some advice based on their famous

corporate portfolio matrix. Your oldest holding, Taco Rocket, has

not grown much in recent years, but due to low debt, it generates

a huge amount of cash. According to BCG$,$ Taco Rocket would be

considered a $\_\_\_\_\_\_\_\_\_\_\_\_.$

a$.$ cash cow

b$.$ star

c$.$ question mark

d$.$ dog

e either star or question mark