Phrase "marriage proposal as long as you promise"

[Elita]

English Language Tests, Intermediate level

ESL/EFL Test #153 "Comparison with as .... as", question 6

I will accept your marriage proposal ......... you promise to love me and take care of me forever.

(a) as good as
(b) as long as
(c) as soon as
(d) as much as

English Language Tests, Intermediate level

ESL/EFL Test #153 "Comparison with as .... as", answer 6

I will accept your marriage proposal as long as you promise to love me and take care of me forever.

Correct answer: (b) as long as
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I don't understand this exercises , Cam you explain to me, please?

Elita

[Mister Micawber]

.
As long as = provided that.
.
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Native English teacher at Mister Micawber's