Understanding textual structure

The structure of a text — its punctuation and connectors — shows how the ideas fit together.
Recognizing these signals helps you predict what a missing word or phrase must be.

A colon is a powerful signal.
Whatever follows a colon explains, defines, or gives an example of what comes just before it.
So the part after the colon is a direct clue to the part before it.

This is very useful for vocabulary-in-context blanks.
If a blank is followed by a colon and then an explanation, the blank must match that explanation.
Read what comes after the colon, then choose the word that fits it.

Other marks work as structural signals too.
A dash can add or explain extra information, and a semicolon joins two complete, closely related ideas.
Noticing these marks tells you how the pieces of a sentence relate.

Choose the word that best fits the blank.
"The parasite presents a remarkable ______: it is the first known animal to completely lack mitochondria."
(A) exception
(B) similarity
The colon means the part after it explains the blank.
Being the first animal to lack mitochondria makes it unusual, so the blank must mean something rare.
Choice (A), "exception", fits; "similarity" is the opposite.

Choose the word that best fits the blank.
"The bird's calls are highly ______: the same species can produce dozens of very different sounds."
(A) consistent
(B) variable
The colon introduces an explanation of the blank.
Producing dozens of different sounds describes something that changes a lot.
So (B), "variable", fits, while "consistent" contradicts the explanation.

Choose the word that best fits the blank.
"The results were ______ — every single trial produced the exact same outcome."
(A) unpredictable
(B) uniform
The dash introduces an explanation of the blank.
Every trial giving the same outcome describes results that are all alike.
So (B), "uniform", fits; "unpredictable" contradicts it.