Which one of the following is an example of an artificial sweetener?

Streptomycin is effective in the treatment of

Ofloxacin is

Heroin is a derivative of:

Tincture of iodine is

Given below are two statements,one is labelled as Assertion $A$ and the other is labelled as Reason $R$.
Assertion $A$: Butylated hydroxy anisole when added to butter increases its shelf life.
Reason $R$: Butylated hydroxy anisole is more reactive towards oxygen than food.
In the light of the above statements,choose the most appropriate answer from the options given below: