Hello Everyone!

Let's tackle this question, one problem at a time, and narrow it down to the right answer! First, here's the original question with any major differences between the options highlighted in orange:

Digging in sediments in northern China, evidence has been gathered by scientists suggesting that complex life-forms emerged much earlier than they had previously thought.

(A) evidence has been gathered by scientists suggesting that complex life-forms emerged much earlier than they had
(B) evidence gathered by scientists suggests a much earlier emergence of complex life-forms than had been
(C) scientists have gathered evidence suggesting that complex life-forms emerged much earlier than
(D) scientists have gathered evidence that suggests a much earlier emergence of complex life-forms than that which was
(E) scientists have gathered evidence which suggests a much earlier emergence of complex life-forms than that

After a quick glance over the options, a few things jump out that we can focus on:

1. Starting with evidence vs. scientists
2. Using suggesting / suggests / that suggests / which suggests
3. Ending with than they had / than had been / than / than that which was / than that

Let's start with #1 on our list because no matter which one we choose, we'll throw out 2-3 options right away. If we look at the sentence as a whole, we see that it starts with a modifier:

Digging in sediments in northern China, evidence has been gathered by scientists suggesting that complex life-forms emerged much earlier than they had previously thought.

We know that whenever we use a modifier, the person/thing/word it's referring to MUST be directly before or after it. So - what/who is digging sediments in northern China? The scientists, or the evidence? The scientists! Let's see which options place the scientists directly after the modifier:

(A) evidence has been gathered by scientists suggesting that complex life-forms emerged much earlier than they had
(B) evidence gathered by scientists suggests a much earlier emergence of complex life-forms than had been
(C) scientists have gathered evidence suggesting that complex life-forms emerged much earlier than
(D) scientists have gathered evidence that suggests a much earlier emergence of complex life-forms than that which was
(E) scientists have gathered evidence which suggests a much earlier emergence of complex life-forms than that

We can rule out options A & B because they don't place the scientists directly next to the phrase that's modifying them.

Now that we only have 3 options left, let's look at #3 on our list: how they end the phrase. It looks like some of them use the pronoun "that," while others don't. Let's take a closer look at each option to make sure the pronoun "that" is clearly referring back to something. If it's not, then we must rule it out!

(C) scientists have gathered evidence suggesting that complex life-forms emerged much earlier than
This is CORRECT! There is no pronoun here to confuse readers. It's clear, concise, and conveys the most logical meaning.

(D) scientists have gathered evidence that suggests a much earlier emergence of complex life-forms than that which was
This is INCORRECT because it has the vague pronoun "that." It's not entirely clear what "that" is referring to here: evidence, complex life-forms, scientists? If it's not 100% clear, it's not a good idea to include the pronoun!

(E) scientists have gathered evidence which suggests a much earlier emergence of complex life-forms than that
This is INCORRECT because it uses the vague pronoun "that." It's also awkward to say "than that previously thought," so let's also rule this one out.

There you have it - option C is the best choice! It places the antecedent next to the modifier and doesn't use vague pronouns, making this option the clearest and most concise option!


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