are a form of web logging in which posts are quite short, containing a brief sentence fragment and, at times, a link to another web resource or video.
a) Hashtags
b) Instant messages
c) Mashups
d) Microblogs

d) Microblogs

Explanation:

A hashtag is indicated by a keyword prefixed by a # on social networking websites. Instant messages consists of real time text based interactions over a network. Mashups are usually used to blend to or more prerecorded songs.

However, Microblogs are a form of web logging that have short short pieces of content designed for quick audience interactions and can easily link to another web resource or video.