It seems that you have already filled the correct pronoun in the blank provided. Yes, the correct answer to complete this sentence is the pronoun "this". The pronoun "this" is an example of a demonstrative pronoun. Other demonstrative pronouns also include these, those, and that. Hope this answer helps.
Correct answer # 2: The world's nations must cooperate; one nation cannot solve the world's problems by itself.
When you connect two related independent clauses or sentences you use a semicolon. Both sentences should be completed grammarly writtend and with a connection. Make sure you do not write a capital letter after the semicolon, unless it is a proper name.
Answer # 3 is incorrect as there is a capitalized word
Answer # 1 it is incorrect to use "for" as the sentence is grammarly completed
The answer is C. A comma must be placed after house and directions.
In your essay give specific details and don't vague if it is not related to the topic you are writing about, is not important.