The work functions of Caesium (Cs), Potassium (K) and Sodium (Na) are $2.14\text{eV}$, $2.30\text{eV}$ and $2.75\text{eV}$ respectively. If incident electromagnetic radiation has an incident energy of $2.20\text{eV}$, which of these photosensitive surfaces may emit photoelectrons?

1. A
   Cs only
2. B
   Both Na and K
3. C
   K only
4. D
   Na only