Example of an insert text question

1 – Read the paragraph

Extinct but already fully marine cetaceans are known from the fossil record. 1 How was the gap between a walking mammal and a swimming whale bridged? 2 Missing until recently were fossils clearly intermediate, or transitional, between land mammals and cetaceans. 3 Very exciting discoveries have finally allowed scientists to reconstruct the most likely origins of cetaceans. 4 In 1979, a team looking for fossils in northern Pakistan found what proved to be the oldest fossil whale.

2 – Read the question and answer options

Look at the part of the passage that is displayed above. The numbers (1), (2), (3), and (4) indicate where the following sentence could be added. 

This is a question that has puzzled scientists for ages.

Where would the sentence best fit?

Choice (1)
Choice (2)
Choice (3)
Choice (4)

Answer:

You can see by the text of the given sentence that there should be a question right before it. And here (right before the placeholder 2) you have it:
How was the gap between a walking mammal and a swimming whale bridged? 2

In this case, we see that option two is the correct one:
How was the gap between a walking mammal and a swimming whale bridged? This is a question that has puzzled scientists for ages.

To make it sure we can try the given sentence in other placeholders:

1 – Extinct but already fully marine cetaceans are known from the fossil record. This is a question that has puzzled scientists for ages.

3 – Missing until recently were fossils clearly intermediate, or transitional, between land mammals and cetaceans. This is a question that has puzzled scientists for ages. Very exciting discoveries have finally allowed scientists to reconstruct the most likely origins of cetaceans.

4 – Very exciting discoveries have finally allowed scientists to reconstruct the most likely origins of cetaceans. This is a question that has puzzled scientists for ages. In 1979, a team looking for fossils in northern Pakistan found what proved to be the oldest fossil whale.

And as we can see none or the options above makes sense.