Choose the complex sentence. - The children jumped into the cool lake, ready to feel refreshed.
- O Marilyn took a wide turn on the water, and she stayed afloat.
- Because of the rough water, skiing was quite difficult.
We need to park the boat at the dock before the sun sets.

D

Explanation:

The children jumped (major clause) (into the cool lake - adverb phrase - where did they jump) ready to feel refreshed. ready is a verb, but there is no subject. The subject is understood to be the children. At best it is a compound sentence.

The second one is also a compound sentence (and it is clear).

Marilyn took a wide turn on the water and

She stayed a float.

Because of the rough water (this is a phrase -- there is no verb).

skiing was quite difficult. This is the main sentence.

We need to park the boat at the dock    main clause

before the sun sets.     Subordinate clause beginning with before

This is your answer.

A mystery surrounds Jesse James’s corpse.

Explanation:

The line "But was the corpse under the marker really him? ' indicates that we don't really know if it's James or not.

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