Ophthalmic solutions should be formulated to include which of the folloeing

Ophthalmic solutions should be formulated to include which of the folloeing?
i|. Sterility
i||. Isotonicity
i|||. Buffering

a- |. Only
b- ||. Only
c- |. And || only
d- ||. And |||. Only
e- |, || and |||***