An Employer Identification Number $($EIN$)$:

a$.$ serves the purpose of identifying sole$-$proprietorships to revenue authorities.

b$.$ is used by the governments of many countries for official paperwork.

c$.$ is a means of disbursing Social Security henefits.

d$.$ is a unique nine$-$digit number issued by the IRS to business entities for purposes of identification.

e$.$ has become a de facto national identification number.