Sambon
can't "allergy to meat" also function as an object of the verb "believe"? Using "allergy to meat" as an object, the sentence would essentially say "Scientists believe allergy to meat to be turning into an epidemic" (Scientists believe X to be Y). Interpreted this way, the sentence has not a grammatical issue but a meaning issue i.e., how can scientists believe an allergy to be something?
In summary, is it fair to say that we should not eliminate answer choice (A) for the reason that it lacks a verb?
A:
an allergy that scientists believe to beThis construction is grammatically valid.
Analogous examples from the web:
items that experts believe to be most importanta wasting syndrome epidemic that scientists believe to be the largest marine wildlife disease event in historybehaviors that psychologists believe to be expressions of a given traitThe issue in A is not grammatical but semantic.
The idiom here is
X believes Y to be Z.
In each of the web examples above, the blue portion -- Z -- expresses what is thought to be a GENERAL TRUTH.
A general truth is a statement that is true not at a particular moment but that is ALWAYS true.
Generally:
When this idiom is properly used, the Z-portion should be something thought to be a general truth.
Back to option A:
an allergy that scientists believe to be turning into an epidemicThe full verb in the red portion is not
to be but
to be TURNING.
to be turning is not a general truth.
Quite the opposite: this construction expresses a TEMPORARY action that is happening RIGHT NOW.
Since the Z-portion in A is not something thought to be a general truth, the idiom
X believes Y to be Z seems misused.