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Can I say,

(a) The hippopotamus lives / stays on / in (the) water.

(b) The cheetah is a fastest on (the) land.
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Vincent TeoCan I say,

(a) The hippopotamus lives / stays on / in (the) water.

(b) The cheetah is a fastest on (the) land. is the fastest [animal] on land

Comments  
Students: We have free audio pronunciation exercises.
Can I say,

(a) The hippopotamus are living in the water.

(b) The hippopotamus are swimming in water.

(c) The hippopotamus are in the water.

(d) The hippopotamus are bathing in water.
Are they correct?
Vincent TeoCan I say,

(a) The hippopotamus are living in the water.

(b) The hippopotamus are swimming in water.

(c) The hippopotamus are in the water.

(d) The hippopotamus are bathing in water.

If these are relating to specific animals:
"The hippopotamus" = one hippo
"The hippopotami" = more than one hippo.

Your verb is plural.
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