.
You need to have a connected graph with no repeating vertices.
The only correct answer is B.
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The answer by @131423324 is wrong.
The short characteristic to person @131423324:
Submitted 3 (three) posts for now.
In two of them he simply re-wrote from @josgarithmetic;
his third post is here and is INCORRECT.
WEB-site, which he announced as "his" in his self-description, does not work.
Should I add something/anything to it ?
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Hey, @131423324, at this forum WE DO NOT NEED such "tutors" . . .