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.

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

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.  

the tariff was created to protect industry in the northern part of the united states. industries in the north were being driven out of business by imported goods that were priced at a low rate. the goal was to protect these industries   by taxing the goods.

answer: (fluidity)is the correct answer.

explanation: because of this characteristic, success on the battlefield depends in large part on the ability to adapt to proactively change events to our advantage as well as to react quickly to constantly changing conditions