Answer:
Man.
Explanation:
A root word can be defined as a word origin for other words in English language.
The common root in manual, manuscript, manufacture, and manicure is man. Man is a word derived from Latin and it simply means hand. Thus, it originated from Ancient Rome.
I. Manual: to perform a task with the hand such as manual labor.
II. Manuscript: a literary document written with hand.
III. Manufacture: it involves the process of producing using the hands.
IV. Manicure: it deals with taking care of the nails and hand.