Is the "s" with apostroph a mistake?

[English Learner]

English Language Tests, Intermediate level

ESL/EFL Test #235 "Phrasal Verbs and Traveling", question 8

Helen went to Italy this spring. Before she was scheduled to leave the country, she decided to ......... in Tuscany for awhile. She's hasn't returned yet because she likes it so much.

(a) stop off
(b) stop over
(c) stop down
(d) stop on

English Language Tests, Intermediate level

ESL/EFL Test #235 "Phrasal Verbs and Traveling", answer 8

Helen went to Italy this spring. Before she was scheduled to leave the country, she decided to stop off in Tuscany for awhile. She's hasn't returned yet because she likes it so much.

Correct answer: (a) stop off

Your answer was: incorrect
Helen went to Italy this spring. Before she was scheduled to leave the country, she decided to stop over in Tuscany for awhile. She's hasn't returned yet because she likes it so much.
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"She's hasn't returned yet because she likes it so much." Is the "s" with apostroph a mistake?

[Yankee]

.
You're right. The 's should not be there. Thanks for pointing that out.
The sentence should be:
She hasn't returned yet because she likes it so much.

Amy
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"Nearly all men can stand adversity, but if you want to test a man's character, give him power." ~ Abraham Lincoln

[Mickey]

What is the differences between stop off and stop by?

[Gheon]

I'd rather ask what is the difference between stop off & stop over, 'cause my dictionary says they both fit there (and have almost the same meaning)?!
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I find your Lack of Faith disturbing!
The Force is out there!

[Beeesneees]

These are how I would use them:
"stop by" - just called in briefly.
"stop off" - break a journey to one place to stay at another.
"stop over" - stay a period of at least one night in a place.
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Cheers m' dears!