Final answer:
The sentence "the hikers knew that the hike was six miles, that it usually required the entire day, and to start after 10:00 a.m. would not be wise" has poor parallel structure due to the last element starting with an infinitive phrase instead of following the pattern set by the first two elements. To create parallelism, all elements should begin with 'that,' such as in the corrected sentence: "The hikers knew that the hike was six miles, that it usually required the entire day, and that starting after 10:00 a.m. would not be wise."
Step-by-step explanation:
The sentence in question has poor parallel structure due to the mismatched construction of its list elements. In the sentence "the hikers knew that the hike was six miles, that it usually required the entire day, and to start after 10:00 a.m. would not be wise", the parallelism is broken by the last part of the list. The first two parts begin with 'that' and describe the hike, but the last part suddenly shifts to an infinitive phrase ('to start after 10:00 a.m.') which disrupts the symmetry of the sentence structure.
To correct the parallel structure, the sentence should maintain a consistent pattern. Here is the revised sentence with correct parallel structure: "The hikers knew that the hike was six miles, that it usually required the entire day, and that starting after 10:00 a.m. would not be wise." In this version, each element in the list begins with the word 'that', creating a balanced and parallel construction.