Question

although prohibitively expensive at first,
which choice completes the text so that it conforms to the conventions of standard english?
choose 1 answer:
a some libraries now own three - dimensional printers, industrial robots which can produce a huge variety of objects.
b three - dimensional printers, industrial robots which can produce a huge variety of objects, are now available at some libraries.
c three - dimensional printers are now available at some libraries, industrial robots which can produce a huge variety of objects.
d some libraries, industrial robots which can produce a huge variety of objects, now own three - dimensional printers.

Explanation:

To solve this, we analyze the logical subject - verb agreement and the correct modification of the noun. The phrase "Although prohibitively expensive at first" should modify the subject "three - dimensional printers" (since they were expensive). Option B has "three - dimensional printers" as the subject, and the non - restrictive clause "industrial robots which can produce a huge variety of objects" correctly modifies "three - dimensional printers" (by providing more information about them), and the sentence structure is correct with "are now available at some libraries" completing the thought. Option A has "some libraries" as the subject, but libraries aren't the ones that were prohibitively expensive. Option C has a comma splice - like error in the structure as it tries to connect two independent - like parts without proper coordination. Option D has an illogical structure where "industrial robots" are incorrectly associated with "some libraries" owning printers.

Answer:

B. three - dimensional printers, industrial robots which can produce a huge variety of objects, are now available at some libraries.