$(a)$ Name a worm which is found in our small intestine.
$(b)$ Name the bacteria which can cause acne.
$(c)$ Which protozoan is responsible for sleeping sickness?
$(d)$ Which disease is caused by the protozoan Leishmania?

(N/A) The worm found in the human small intestine is the Roundworm, scientifically known as $Ascaris lumbricoides$.
$(b)$ The bacteria responsible for causing acne is $Staphylococcus$ (specifically $Staphylococcus epidermidis$ or $Staphylococcus aureus$ strains).
$(c)$ The protozoan responsible for sleeping sickness is $Trypanosoma$ (specifically $Trypanosoma brucei$).
$(d)$ The disease caused by the protozoan $Leishmania$ is Kala-azar (also known as visceral leishmaniasis).