Final answer:
Henry likely caught the flu through direct transmission by either touching a contaminated surface like a doorknob or through direct contact, such as shaking hands with an infected person.
Step-by-step explanation:
Henry could have likely acquired the flu through direct transmission in any of the scenarios mentioned, as the flu can be spread by both contact with contaminated surfaces and direct contact with an infected person.
Specifically, touching a doorknob immediately after an infected person (contact transmission) or shaking a client's hand (direct contact) both represent probable ways in which Henry could have contracted the virus.
It's important that to prevent the spread of pathogens like the flu virus, regular and thorough hand washing is a crucial practice.