Christmas cards is it "The Smiths" or "The Smith's"

[Duo]

English Language Tests, Intermediate level

ESL/EFL Test #551 "English Slang Idioms (293)", question 1

"I am sorry that my mother made that off-the-......... comment to you about seeing your family. I know that she doesn't mean that you shouldn't see your family and that you should only see ours. I think she was trying to make a joke and, at the same time, tell you that she likes having you here in her own strange way," Brent said to Lisa.

(a) whack
(b) parapet
(c) wall
(d) shoe

English Language Tests, Intermediate level

ESL/EFL Test #551 "English Slang Idioms (293)", answer 1

"I am sorry that my mother made that off-the-wall comment to you about seeing your family. I know that she doesn't mean that you shouldn't see your family and that you should only see ours. I think she was trying to make a joke and, at the same time, tell you that she likes having you here in her own strange way," Brent said to Lisa.

Correct answer: (c) wall
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If I am sending Christmas cards is it "The Smiths" or "The Smith's"

Duo

[Alan]

Hi,

All you need here is an 's' on its own to show the plural.

Alan
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English as a Second Language
You can read my ESL story French or English?