"The use of standard marks and signs in writing and printing to separate words into sentences, clauses and phrases in order to clarify meaning."
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"The correct and consistent use of punctuation is an essential aspect of a teacher's literacy; clear writing demands the ability to understand and apply the rules of punctuation.
In the test
There are 15 instances of punctuation that need to be inserted, you are not required to remove or rewrite sections of the passage.
The passage may contain instances where punctuation is acceptable although not essential; nonessential punctuation will not attract extra marks, nor will marks be deducted."
(Information from education.gov.uk)
Punctuation is the difference between knowing your nuts and knowing you're nuts!
it will help you practise the use of commas.
If you are really stuck for a basic guide follow this link to the Punctuation Pyramid.
Consult this first: Basic Punctuation Guide - Unravelling the confusion between colons, semi-colons, commas etc.
Spot the commas - Place the commas in the correct places.