The surface of a metal plate is illuminated with light of a certain frequency. Which of the following conditions determine whether or not photoelectrons are ejected from the metal?

1. The number of photons per second emitted by the light source

2. The length of time that the light is turned on

3. The thermal conductivity of the metal

4. The surface area of the metal illuminated by the light

5. The type of metal from which the plate is made

(a) 1 and 2 

(b) 5 

(c) 3 and 5 

(d) 4 

(e) 2 and 3