The ﬁeld of geological oceanography owes much to American ______ Marie Tharp, a pioneering oceanographic cartographer
whose detailed topographical maps of the ocean ﬂoor and its multiple rift valleys helped garner acceptance for the theories
of plate tectonics and continental drift.
geologist,
geologist
geologist;
geologist:
Choice B is the best answer. “Marie tharp” is essential information that completes the ﬁrst clause — the ﬁrst clause doesn’t
function without it. So we don’t want to separate it with punctuation. 
Choice A is incorrect. This choice creates a punctuation error. “The ﬁeld of geological oceanography owes much to
American geologist” is unclear: which geologist are we talking about? We need the “Marie Tharp” for clarity, which means it’s
essential information and should not be separated by a comma. Choice C is incorrect. This choice creates a punctuation
error. “The ﬁeld of geological oceanography owes much to American geologist” is unclear: which geologist are we talking
about? We need the “Marie Tharp” for clarity, which means it’s essential information and should not be separated by a
semicolon. Choice D is incorrect. This choice creates a punctuation error. “The ﬁeld of geological oceanography owes much
to American geologist” is unclear: which geologist are we talking about? We need the “Marie Tharp” for clarity, which means
it’s essential information and should not be separated by a colon.