Answer: The sentence that needs to be revised in order to make the language more formal is (3) A mission specialist gets to do assigned tasks and cool stuff like using the robotic arm, going on spacewalks and doing science experiments.
Step-by-step explanation: It is highly important to use formal language when working on an academic piece of writing such as an essay. Therefore, it is fundamental to avoid the use of contractions and informal words. Sentence (3) has been written in an informal language since it includes words such as "get", "cool" and "like". Therefore, this sentence needs to be revised in order to make the language more formal. A good way of improving this sentence is writing "A mission specialist carries out assigned tasks by using the robotic arm, going on spacewalks and doing science experiments".