Milk turns into curd sue to action of

Question

$\begin{array}{1 1} (a)\; \text{Bacteria called Lacto bacilli } \\ (b)\; \text{Protozoan called paramecium} \\ (c)\; \text{A fungus called Penicillium } \\ (d)\; \text{A blue green algae called Nostoc }\end{array}$