Psychiatrist: Take any visceral emotion you care to consider.
Conclusion (So)
There are always situations in which it is healthy to try to express one's anger.
Evidence
There are always situations in which it is healthy to try to express [any visceral emotion you care to consider].
Evaluate / Goal
Given the parallel structure of the evidence and the conclusion, we're just trying to match up where they diverge.
If the argument is saying, , then the missing assumption is "Coke is delicious".
Since the argument is saying, , then the missing assumption is "Anger is a visceral emotion".
The correct answer definitely has to have "anger" in it, since we're trying to prove a conclusion about "anger" but received no facts (i.e. premises) so far about "anger".