Answer:
<u>“that activity can be justified by no one”</u>
Explanation:
Whether a piece of writing is formal or informal depends on the choices of vocabulary, the way it is organized and the tone.
We use formal English when we talk or write in a polite, and more proper manner, with descriptive, precise and elegant words (that we do not tend to use so often in our everyday life) and with longer sentences (which often includes passive voice sentences). This tone is totally free from idioms, colloquialism, slang, and contractions, and we do not usually use first-person pronouns.
So, from all the given options, “that activity can be justified by no one” is the one that uses formal English because it is written in a more elegant manner, the words are precise, it uses the passive voice and it does not have first-person pronouns nor contractions.