Balantidium & Opalina are included in class:

Explanation

The correct answer is Ciliata. Balantidium and Opalina are ciliated protozoans, meaning they use cilia for movement and feeding, which is a defining characteristic of the class Ciliata. This distinguishes them from other classes of protozoans like Flagellata, which use flagella; Sarcodina, which use pseudopodia; Sporozoa, which are mostly non-motile; and Suctoria, which use tentacle-like structures instead of cilia in their feeding process.