He had to curtail his leave as a lot of work was pending in his office.

Answer: Option C

Cancel : decide or announce that (a planned event) will not take place.
Extend : cause to cover a wider area; make larger.
Shorten : make or become shorter.
Postpone : cause or arrange for (something) to take place at a time later than that first scheduled.
Curtail : reduce in extent or quantity; impose a restriction on.

Synonym of Curtail is Shorten