Read this example of incorrect sentence structure.

Heavy, black clouds rushing in from the horizon.

Which revision corrects the sentence?

O Heavy, black clouds rushing in from the horizon, get under cover.

O Heavy, black clouds rushing in from the horizon. It's about to rain.

Heavy, black clouds rushing in from the horizon when it's about to rain.

O Heavy, black clouds rushing in from the horizon mean a storm is coming.

Heavy, black clouds rushing in from the horizon mean a storm is coming.

Explanation:

The sentence fragment given does not express a complete thought. In fact, it is a noun phrase that could function as the subject of a sentence. Therefore, it must join a predicate in order to make sense.

The rest of the alternatives are incorrect because the sentence fragment still does not represent a complete idea and the argument is not logically consistent. The reason is that the options consist of either another sentence fragment, an independent clause and a subordinate clause.

Heavy, black clouds rushing in from the horizon mean a storm is coming.