Which of the following best defines the underlined word in the sentence below: “ John was very upset when he received his summons in the mail.”
A.
a non-mandatory notice to answer a complaint
B.
a non-mandatory request for mediation
C.
a mandatory request for arbitration
D.
a mandatory notice to defend oneself against a complaint

D. a mandatory notice to defend oneself against a complaint

Explanation:

In legal terms, the word "summons" means a legal notification that is given  to the accused that he/she has been sued. The notification will consist of the time and date where the accused is expected to come for their legal proceedings.

Summons are mandatory. If you are ignoring summons, the court has the authority to send out a warrant to arrest you. This tend to increase the amount of punishment that you would get if you are proven guilty.