roll vs walk

[Homo]

English Language Proficiency Tests, Advanced Level

ESL/EFL Test #29 "Letter Writing (1)", question 7

The first time I tried to use it, your lawnmower simply ......... over the grass but did not cut it.

(a) walked
(b) rolled
(c) strode
(d) tripped

English Language Proficiency Tests, Advanced Level

ESL/EFL Test #29 "Letter Writing (1)", answer 7

The first time I tried to use it, your lawnmower simply rolled over the grass but did not cut it.

Correct answer: (b) rolled
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Why is not walked?

Homo

[Alan]

'Walked' means use your feet to continue and so can't be used for a machine.

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