Besides the force due to gravity or g, what else determines the period of a pendulum?

For a simple pendulum, the mathematical equation that describes the period (T) is T=√(l/g) where l is the length of the string and g is the acceleration due to gravity (9.81 metres per second). Therefore it can be seen that both gravity and the length of the string within a pendulum effects its period. 

The answer is d) by requesting advice on science internet sites