Perhaps he meant that they both understood what the other character or thing was saying, without saying a word
I believe the answer is individuals. The drug side effect is the result of the interaction from the substance contained by the drugs and the environment in our body. It means that the effect will be influenced by the individual's age, weight, height, gender, etc.
"Whoa there, buddy," Leticia cautioned, "Let's not jump to any conclusions."
Which would also be #2.
It would seem to be C because he choose that field and since it’s unionized he is having a hard time finding a open spot