Which of the following is an internal event?
a.
an indoor company-sponsored concert that's open to the public
b.
a store sale
c.
a company picnic for employees
d.
a limited time coupon mailed to potential customers

The correct answer is "C.  A company picnic for employees".

Explanation: An internal event is an event to which only people belonging to the same entity, institution or company can attend. For example A company picnic for employees.

An external event is that event in which not only members or employees of a company can attend but also an external public that does not belong to the company in question. For example: An indoor company-sponsored concert that's open to the public.