Answer:
A. a false generalization
Explanation:
All people who work do so in an office, at a computer. Bill works, so he works in an office, at a computer.
This is false generalization.
A false generalization is a mistake that we do when we generalize something without considering all the points or variables.
Like here, if people work, that does not generally means they always work in offices and work in front of computers.
There are many professions like various sports, civil engineering, police patrolling etc that cannot be done while sitting in an office and in front of a computer.
Hence, option A is the answer.