An innovative tool that is rapidly gaining in popularity

My answer is (C). It took me 02:13.

The sentence starts with an appositive “An innovative tool...”, so the subject should be "a 3-D printer" instead of "3-D printers". Eliminate (A) and (B).

To provide examples, we use "such as". Eliminate (D). (D) also contains comma splice.

Now, between (C) and (E), (E) is longer without gaining any clarity. If anything, the antecedent for "they" can be ambiguous. So, (C) wins.

Still, I wonder how a 3-D printer can create fossils of million years old?
And, should we use hyphen between million, year, and old?

C is the answer.
Rest can be eliminated due to inclusion of "including million year old fossils" which is illogical. Do printers include million year old fossils? No. And E can be eliminated due to use of "they".

Imo the answer is C.

Pre-thinking error: A seems fine on the up but has few minor errors compared to C.

For introducing examples usage of 'such as' is better than including. In addition, an innovative tool should describe a 3D printer rather than 3D printers.

An innovative tool that is rapidly gaining in popularity, 3-D printers allow engineers to create customized three-dimensional objects, including million year old fossils and prosthetic limbs, at a lower cost and of higher quality than in the past.

A) 3-D printers allow engineers to create customized three-dimensional objects, including million year old fossils and prosthetic limbs, at a lower cost

B) 3-D printers allow engineers to create customized three-dimensional objects, including million year old fossils and prosthetic limbs, and they can do it at a lower cost

*) "An Innovative tool that is".... This opening modifier should modify a singular noun. By looking at the options, (A) and (B) can be eliminated because they both (A) and (B) have plural noun "3-D printers".

*) Both Such as and Including can be used to introduce examples. So, there should be other errors which will help us to eliminate 2 options.

C) a 3-D printer allows engineers to create customized three-dimensional objects, such as million year old fossils and prosthetic limbs, at a lower cost
This does not have any pronouns to create any errors. The opening modifier is correctly referring to the singular "A 3-D printer". If you cross off the list of items, the sentence says "a 3-D printer allows engineers to create customized three-dimensional objects at a lower cost". This sentence makes much sense. So, this is correct.

D) a 3-D printer allows engineers to create customized three-dimensional objects, including million year old fossils and prosthetic limbs, engineers can do this at a lower cost
"Engineers can do this at a lower cost". What does "this" refer to? Also, I am a bit confused about the logic.


E) a 3-D printer allows engineers to create customized three-dimensional objects, such as million year old fossils and prosthetic limbs, which they can do at a lower cost
I am not quiet sure what "They" is referring to. "They" can refer to bunch of items, such as engineers and three-dimensional objects. It's confusing and illogical. So, eliminate E.

Answer C

Here, million year old fossils and prosthetic limbs are examples therefore "such as" is the preferable term.
Eliminate (A),(B) and (D)
and "An innovative tool...." should be "a 3-D printer"
Eliminate (A) and (B)

Only one option is left (C)
Answer: (C) a 3-D printer allows engineers to create customized three-dimensional objects, such as million year old fossils and prosthetic limbs, at a lower cost