Select the most appropriate option of the given word to fill in the blank.
The new construction sites have ________ attack by the environmentalists.

The correct answer is come under.

Explanation:

Let's understand the meaning of the phrasal verbs given in the options:

1. Come under: To experience or be subjected to something (often negative, such as attack, criticism, scrutiny, or pressure). For example, "The company came under criticism for its policy." In the context of the sentence, "come under attack" correctly conveys that the new construction sites were subjected to attack/criticism by environmentalists.

2. Come off: To succeed, happen, or become detached/separated from something.

3. Come upon: To meet, find, or discover someone or something by chance.

4. Come out: To be published, released, or become known.

Therefore, the most appropriate phrasal verb to fill in the blank is come under, making the complete sentence: "The new construction sites have come under attack by the environmentalists."