Answer:
-Warning: If taken internally, consult a physician immediately.
Explanation:
A colon is a grammatical punctuation mark used in sentences for the separation between an independent clause and the dependent clause. But more importantly, they are used to separate such clauses when the second clause is used to explain the first clause.
Among the given examples, the correct usage of the colon is in the first sentence.
<u><em>Warning: If taken internally, consult a physician immediately.</em></u>
While the other sentences are normal, regular sentences The use of this mark in the other two sentences, especially the placing of it in a free flowing sentence is wrong. As for the first option, the colon just after "warning" emphasizes the importance of the given information. Also, the next sentence after the colon mark gives an explanation of why the first part of the sentence is used.
