• Ancient Romans found it therapeutic to bathe in cold milk, in strawberries that had been crushed, or in bathtubs filled with black caviar
The sentence presents list of things that the ancient Romans considered therapeutic to bathe in:
a. Cold milk.
b. Strawberries that had been crushed, or
c. in bathtubs filled with black caviar
None of the entities are grammatically parallel in this list. The first one is just a noun entity, the second one a noun followed by relative pronoun clause, and the third a noun followed by a prepositional phrase. Notice that grammatically, it is possible to make all the three entities identically parallel. They all can be written in the form of the first entity.
Logically too, these entities are not parallel. The first two entities are the ingredients considered to be therapeutic. However, the third entity says “in bathtubs”. Now, “bathtubs” are not the ingredients of therapeutic bath. The ingredient is “black caviar”. Hence that should follow “in” to make the list logically parallel.
Now let’s run the POE:
A) to bathe in cold milk, in strawberries that had been crushed, or in bathtubs filled with black caviar: Incorrect
for the reasons discussed above. Also, use of past perfect tense “has been crushed” does not make sense here.
B) that they bathe in cold milk, in strawberries that had been crushed, or in caviar that was black: Incorrect.
a. Use of “that” is incorrect here.
b. The last two entities in the list are not parallel to the first entity.
c. Use of “had been crushed” is not correct.
d. Simple present tense “bathe” is also incorrect because we are talking about a past event.
C. to bathe in cold milk, crushed strawberries, or black caviar: Correct.
All the entities are grammatically as well as logically parallel.
D. that they bathe in cold milk, crushed strawberries, or black caviar: Incorrect.
a. Use of “that” is incorrect.
b. Simple present tense “bathe” is incorrect.
E. to bathe in milk , strawberries, or caviar: Incorrect.
This choice removes all the adjectives before the nouns, leading to the change in the intended meaning even if grammatically this choice is correct.
Hope this helps.