Meaning of "walk up"

[Gabi]

English Language Tests, Intermediate level

ESL/EFL Test #101 "Phrasal Verb: Walk", question 7

A total stranger walked ......... to me and asked if I could lend him some money.

(a) along
(b) by
(c) up
(d) under

English Language Tests, Intermediate level

ESL/EFL Test #101 "Phrasal Verb: Walk", answer 7

A total stranger walked up to me and asked if I could lend him some money.

Correct answer: (c) up

Your answer was: incorrect
A total stranger walked along to me and asked if I could lend him some money.
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what is the meaning of "walk up"? Why isn't it in regular dictionaries?

Gabi

[Mister Micawber]

.
Walk up to = walk to the immediate location of.

From the Merriam-Webster Dictionary:

Main Entry: up to
Function: preposition
1 -- used as a function word to indicate extension as far as a specified place <sank up to his knees in the mud>
2 -- used as a function word to indicate a limit or boundary <up to 50,000 copies a month> <worked up to the last minute>
.
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Native English teacher at Mister Micawber's