Which of the following sentences have been correctly punctuated?

some students prefer learning from the textbook others prefer e-learning.

the polar bear, which is an endangered species, lives mostly in the arctic region.

"there i was" murmured the eight year old as he started to think back.

the president said, "stand united and no one can defeat you. victory will be ours"!

allusion is a figure of speech that refers to another work in order to explain an idea.

There are two answers to this question:

Answer 1. The polar bear, which is an endangered species, lives mostly in the arctic region.

Answer 2.Allusion is a figure of speech that refers to another work in order to explain an idea.

Explanation:

Using the correct punctuation mark can improve the clarity of writing.

The sentence "The polar bear, which is an endangered species, lives mostly in the arctic region" has been correctly punctuated because the additional information about the polar bear is correctly separated by commas.

The sentence "Allusion is a figure of speech that refers to another work in order to explain an idea" has been correctly punctuated because two independent sentences have been linked with the pronoun ‘that’ and this eliminates the need to use a comma.

The sentence "The President said, "Stand united and no one can defeat you. Victory will be ours"! is incorrectly punctuated because the exclamation mark is wrongly placed.

The sentence "There I was" murmured the eight year old as he started to think back. is incorrectly punctuated because it misses a comma after the word "was."

The sentence "Some students prefer learning from the textbook others prefer e-learning" has been incorrectly punctuated. The independent clause "others prefer e-learning" should be preceded by a semicolon.  

one of the central themes of edward abbey's work has been his staunch opposition to the glen canyon dam on the colorado river that created lake powell, destroying stunning scenery and wildlife habitat, endangering many rare species of fish and animals, and also irreparably destroying many important archaeological sites which provided information about the early inhabitants of the united states.