Explanation

All of the options listed can be transmitted via infectious droplets:

• Rubella (German measles) is an airborne disease spread through droplets when an infected person talks, coughs, or sneezes.
• Common cold is a viral infection spread through airborne droplets when an infected person talks, coughs, or sneezes.
• Influenza (flu) is also an airborne disease spread through droplets when an infected person talks, coughs, or sneezes.

Infectious droplets are a common mode of transmission for many respiratory pathogens, including viruses and bacteria.

So, none of the above options are incorrect, and the correct answer is indeed "None of the above".