Which of the following sentences includes a pronoun with an unclear antecedent?
a) Members of the US Geological Survey say they believe past earthquakes may have been larger, but the Chilean earthquake is certainly the largest since accurate magnitude measurements were invented.
b) People who have lived through extreme earthquakes report feeling terror and helplessness when the earthquake hits.
c) In places as far away as Japan, they died because of the tsunami caused by the earthquake.
d) The largest twentieth century earthquake, which reached a magnitude of 9.5, occurred in southern Chile.