diffrence between "back down" and "back over"

[Asia]

English Language Tests, Intermediate level

ESL/EFL Test #165 "Phrasal Verbs (A to B)", question 4

Lenny didn't ......... when his superior reprimanded him.

(a) back up
(b) back down
(c) back over

English Language Tests, Intermediate level

ESL/EFL Test #165 "Phrasal Verbs (A to B)", answer 4

Lenny didn't back down when his superior reprimanded him.

Correct answer: (b) back down

Your answer was: incorrect
Lenny didn't back over when his superior reprimanded him.
_________________________

What is the diffrents between " back down " and " back over "

Thanks,
Asia

[Conchita]

back down phrasal verb
to admit that you were wrong or that you have been defeated:
Eventually, Roberto backed down and apologized.
Local residents have forced the local council to back down from/on its plans to build a nightclub in their street.

(from Cambridge Advanced Learner's Dictionary)

Back over: I'm not sure there is such a verb.

[Yankee]

One way I can think of that 'back over' could possibly be used is when 'back' means 'drive your car in reverse' or 'walk backwards' and you then go over something:
Since he couldn't turn his car around, he had to back over the narrow bridge.