How much protein does a $250 \ kg$ cow produce per day (in $g$)?

Which organism is used to obtain the single cell protein?

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

Why are proteins synthesised from Spirulina called single cell proteins?

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.

Which of the following is true regarding Single Cell Protein $(SCP)$?