Step 1: Alexopoulos and Mims' classic 1979 mycology textbook grouped fungi into major classes based largely on their sexual spore type and hyphal organisation.
Step 2: Entomophthorales, the order containing many insect-killing fungi such as Entomophthora, was grouped together with Mucorales under class Zygomycetes because both orders form thick-walled sexual zygospores and have non-septate (coenocytic) mycelium.
Step 3: Oomycetes (water molds), Ascomycetes (sac fungi) and Myxomycetes (slime molds) are separate lineages with different reproductive structures, so none of them is the classification given to Entomophthorales in this scheme.
The correct answer is Zygomycetes.