an analysis – analyses; a basis – bases; a bacterium – bacteria; a crisis – crises; a datum – data.
a man – men; a woman – women; a foot – feet; a tooth – teeth; a mouse – mice; a louse – lice; an ox – oxen; a child – children; a grandchild – grandchildren; a businessman – businessmen.
Исключения: a roof – roofs; a chief – chiefs; a proof – proofs; a gulf gulfs; a grief – griefs; a belief – beliefs; a handkerchief – handkerchiefs.