as long as vs. when

[Maffey]

English Language Tests, Intermediate level

ESL/EFL Test #142 "Time clauses: future tense examples", question 9

I'll give you a ring ......... we get back from our vacation.

(a) while
(b) until
(c) when
(d) as long as

English Language Tests, Intermediate level

ESL/EFL Test #142 "Time clauses: future tense examples", answer 9

I'll give you a ring when we get back from our vacation.

Correct answer: (c) when
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Why not "as long as"?

Maffey

[Yankee]

Hi Maffey

The expression 'as long as' means 'provided that'. Using this expression in the test sentence would suggest that there is a small possibility that you will never return from your vacation, and therefore there is also a possibility that you will never telephone the person.
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