Meaning of "waited on" and "waited in"

[Paporii]

English Language Tests, Intermediate level

ESL/EFL Test #200 "Phrasal Verbs (T to W)", question 3

Krista ......... her ill husband all day long.

(a) waited on
(b) waited in
(c) waited down

English Language Tests, Intermediate level

ESL/EFL Test #200 "Phrasal Verbs (T to W)", answer 3

Krista waited on her ill husband all day long.

Correct answer: (a) waited on
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Please, explain the meaning of "waited on" and "waited in"...

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[Mister Micawber]

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Wait on = serve (as a waiter does)
Wait in is not an idiom; it it just 'wait' + 'in'.
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Native English teacher at Mister Micawber's