Bunuel wrote:
Although most scientists refer to arachnids as a class of insects having eight appendages, a segmented body and no antennae, it has become synonymous with spiders that in reality are just one of the orders in the class, the largest order in it.
(A) it has become
(B) they had become
(C) they have become
(D) they became
(E) becoming
The sentence talks about how most people use the term "arachnids" to refer only to spiders, even though arachnids actually include other creatures with eight legs, a segmented body and no antennae.
The correct answer choice is (C), "they have become", because it correctly uses present perfect tense to indicate that this usage has become common over time. The other answer choices are incorrect because they use past or present tense, which do not convey the same meaning as present perfect.
For example, (A) "it has become" is correct in using present perfect, but it uses the singular "it" to refer to the plural "most scientists," which is grammatically incorrect.
Similarly, (B) "they had become" uses past perfect tense, which suggests that this usage was common in the past but may not be now, while (D) "they became" uses simple past tense, which does not convey the ongoing nature of the usage.
Finally, (E) "becoming" is a gerund form and is not appropriate in this context as it suggests that the usage is actively in the process of becoming something.