Yes, United States would be capitalized always. Even if it is in the middle of a sentence, you still need to capitalize it, because it is a proper noun. There is only one "United States". The common noun of the USA is "countries". There are many, many countries in the world (Brazil, Afghanistan, Britain, USA, etc.) but only one United States of America, which is a specific noun that identifies only one place.
Yes, "United States" should be capitalized in the middle of a sentence as it is a proper noun referring to a specific country. For example: The President of the United States attended the meeting.
No, "secondary students" should not be capitalized in the middle of a sentence unless it is a proper noun or at the beginning of a sentence.
No, "polar" should not be capitalized when used in the middle of a sentence. It should only be capitalized if it is the first word of a sentence or part of a proper noun.
No, "sister" is not capitalized in the middle of a sentence unless it is used as part of the name or title that is capitalized. For example, in "I have a younger sister," "sister" would not be capitalized.
no
No, "narwhal whale" does not need to be capitalized in the middle of a sentence unless it is part of a proper noun or title.
No, "secondary students" should not be capitalized in the middle of a sentence unless it is a proper noun or at the beginning of a sentence.
Dodgeball is capitalized if it starts the sentence. But if dodgeball is used in the middle of a sentence it is not capitalized.
No it shouldn't be capitalized.
No, "sister" is not capitalized in the middle of a sentence unless it is used as part of the name or title that is capitalized. For example, in "I have a younger sister," "sister" would not be capitalized.
No it shouldn't be capitalized.
no
No, "narwhal whale" does not need to be capitalized in the middle of a sentence unless it is part of a proper noun or title.
No, the word "winter" should not be capitalized in the middle of a sentence unless it is at the beginning of a sentence or part of a proper noun.
Yes, "Mars" should be capitalized in the middle of a sentence as it is a proper noun referring to the planet.
No, the word "antibiotic" should not be capitalized in the middle of a sentence unless it is at the beginning of a sentence or part of a proper noun.
No, the word "century" is not capitalized unless it begins a sentence. So "thirteenth century" would not be capitalized in the middle of a sentence.
Yes.