Which is the passive voice of: “A strong firefighter was carrying a child downstairs”?

MCQ Quiz

2. Which is the passive voice of: “A strong firefighter was carrying a child downstairs”?

a
A strong firefighter was being carried downstairs by a child.
b
A child was carried downstairs by a strong firefighter.
c
A child was being carried downstairs by a strong firefighter.
d
A strong firefighter was carried downstairs by a child.