Consider the following statements:
1. The radiation falling on a photodiode is primarily a minority carrier injector.
2. The short-circuit current of a reverse biased photodiode under illumination varies exponentially with light intensity.
3. The photo voltage emf of an open-circuited photodiode varies logarithmically with the light generated short-circuit current.
4. The spectral response of a photodiode does not depend upon the frequency of the incident light.
Which of these statements are correct?

A. 1, 2, 3 and 4

B. 3 and 4 only

C. 1 and 2 only

D. 1 and 3 only

Answer: Option D