Meaning of the word "prowling"

[Dongocan]

Synonym Search, Intermediate level

ESL/EFL Test #110 "Synonyms for wander", question 6

Ann didn't want to leave the house as she was afraid that thieves were ......... in the dark.

(a) walking
(b) strolling
(c) prowling
(d) ranging

Synonym Search, Intermediate level

ESL/EFL Test #110 "Synonyms for wander", answer 6

Ann didn't want to leave the house as she was afraid that thieves were prowling in the dark.

Correct answer: (c) prowling

Your answer was: incorrect
Ann didn't want to leave the house as she was afraid that thieves were walking in the dark.
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i don't know the meaning of the word "prowling" in this sentence. please explain more clearly 4 me. thx in advanced
An

[Gray]

Dictionary says -

Prowling - To roam through stealthily, as in search of prey or plunder

Grammar book says -

I don't know the meaning of the word "prowling" in this sentence. Please explain more clearly for me.

Thanks in advance.
An

:)
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First lesson - English, not english. I, not i. ~A student of English