Explanation
Correct answer: A.
Choice A is the best answer. The convention being tested is the use of verb forms within a sentence. The nonfinite past participle "created" is correctly used to form a supplementary element that modifies the noun phrase "the saloon," identifying who established the Boston Saloon.
Why the other choices are wrong
Choice B
Choice B is incorrect because it results in an ungrammatical sentence. The finite present tense verb "creates" can’t be used in this way to form a supplementary element to modify the noun phrase "the saloon."
Choice C
Choice C is incorrect because it results in an ungrammatical sentence. The nonfinite present participle "creating" can’t be used in this way to form a supplementary element to modify the noun phrase "the saloon."
Choice D
Choice D is incorrect because it results in an ungrammatical sentence. The finite present tense verb "create" can’t be used in this way to form a supplementary element to modify the noun phrase "the saloon."