This is an interesting question to analyze.
A) The couple, like hundreds of other beekeepers in western Canada and the US,
were hunting the Asian giant hornet, an invasive species whose stealthy advance throughout British Columbia and Washington state is causing growing unease.
The answer to the question "Who was hunting" is "The couple", which is a collective noun. On the GMAT, collective nouns are considered singular, since they are thought of as a single group to which all verbs and adjectives are applied. Therefore, the appropriate verb here would be "was hunting". Eliminate.B) The couple, like hundreds of other beekeepers in western Canada and the US,
were hunting the Asian giant hornet, an invasive species whose stealthy advance throughout British Columbia and Washington state
are causing growing unease.
Same error as (A). Also, "stealthy advance" is a singular noun and requires the singular verb "is causing". Eliminate.C) The couple, such as hundreds of other beekeepers in western Canada and the US,
were hunting the Asian giant hornet, an invasive species whose stealthy advance throughout British Columbia and Washington state
are causing growing unease.
Same error as (A) and (B). Eliminate.D) The couple, such as hundreds of other beekeepers in western Canada and the US, was hunting the Asian giant hornet, an invasive species whose stealthy advance throughout British Columbia and Washington state is causing growing unease.
Correct answer. Singular verbs are used for the collective noun as well as "advance". No other errors are introduced.E) The couple, like hundreds of other beekeepers in western Canada and the US, was hunting the Asian giant hornet,
and an invasive species whose stealthy advance throughout British Columbia and Washington state is causing growing unease.
This brings about a shift in meaning, implying that the couple was hunting "an invasive species" in addition to and different from the Asian giant hornet. Eliminate.Hope this helps.