Three fourths of the work done.

1. have been
2. were
3. has been
4. had

Explanation: ভগ্নাংশের ক্ষেত্রে, ভগ্নাংশের সাথে of দ্বারা যুক্ত noun টি singular হলে verb টিও singular হবে ও of দ্বারা যুক্ত noun টি plural হলে verb টিও plural হবে। যেমন- a) One-third of the students are present in the class. b) Three-fourths of the work has been finished.