Answer:
A. Sentence 1.
Step-by-step explanation:
In the given paragraph, the sentence that contains an error is Sentence 1. Sentence 1 is structurally not correct. The first sentence of the paragraph begins with a modifying phrase. A modifying phrase is used to modify or clarify the closet noun, adverb, verb, etc. But the list of modifiers are not modifying the closet noun, that is 'the animal shelter' instead it modifies the work that's been done in an animal shelter.
So, Sentence 1 consists of a structural error. Therefore, option A is correct answer.