SAT Question 003f22c8: Form Structure And Sense answer and explanation

English - Form Structure And Sense - Subject Verb Agreement
0:00
FREE OFFICIAL BANK
Every last second of space shuttle mission STS-79, which lasted ten days and three hours, ______ carefully monitored by a team of experts.
1
Difficulty:Medium
Which choice completes the text so that it conforms to the conventions of Standard English?