Which organism is cultivated as a source of $SCP$?

Consider the following four statements $(1-4)$ and select the option that includes all the correct statements:
$(1)$ The unicellular $Spirulina$ can produce large quantities of food rich in protein,minerals,vitamins,etc.
$(2)$ $Methylophilus$ $methylotrophus$,because of its high rate of biomass production and growth,can produce $25$ tonnes of protein per day.
$(3)$ Common button mushrooms are rich in Vitamin $C$.
$(4)$ Rice varieties have been developed which are rich in calcium.

One of the alternative sources of protein for human and animal nutrition is ........ .

Select the incorrect option regarding Single Cell Protein $(SCP)$.

People recovering from a long illness are often advised to include the alga $Spirulina$ in their diet because it

What contributes to the nutritional value of Single Cell Protein $(SCP)$?