This question seems to appear in a practical English test in the following form:
Which of the following choices best describes the error in this sentence?
The man is a scientist with a keen sense of observation and who dedicates long hours in the lab.
You are then offered the following multiple choice answers:
- Dangling modifier (where a grammatical modifier could be mistakenly assigned to the incorrect subject)
- Uneven parallelism (When phrases or clauses within the same sentence have different grammatical structure)
- Fragment (A sentence that doesn't contain a complete clause)
- Misplaced modifier (The sentence has an unintended meaning because of the placement of a modifier)
I would opt for Answer B - Uneven parallelism, as reading this sentence back, there does seem to be a "disjoin" between the way the two halves of the sentence are structured, as if they don't flow or belong together.
