Which organism is used to obtain the single cell protein?

Consider the following statements $(I-IV)$ and select the option containing the correct answer.
$I.$ The unicellular $Spirulina$ can produce large quantities of food rich in protein,minerals,and vitamins.
$II.$ Based on body weight,the microorganism $Methylophilus$ $methylotrophus$ can produce much more protein in a day than a cow.
$III.$ Common button mushrooms are a rich source of Vitamin-$C$.
$IV.$ $A$ variety of rice has been developed that is rich in calcium.

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

What is the full form of $SCP$?

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

Given below are two statements with respect to single cell protein.
Statement $I$: Single cell protein refers to the crude,or refined edible protein,extracted from pure microbial cultures or from dead or dried cell biomass.
Statement $II$: $SCP$ can be readily used as fodder for achieving fattening of calves,pigs,in breeding fish and in poultry.
In the light of the above statements,choose the correct answer from the options given below.