Question #N189

The first time that the United States successfully launched a rocket into space was in 1958. That event, which some historians consider the start of the space race, was a major turning point in human history.

Which choice best combines the sentences at the underlined portion so that it conforms to the conventions of Standard English?
A. That event, some historians consider the start of the space race, was a major turning point in human history.
B. That event, which some historians consider the start of the space race, was a major turning point in human history.
C. That event some historians consider the start of the space race, was a major turning point in human history.
D. That event, some historians consider the start of the space race, was a major turning point in human history.