Difference between 'if', 'as' and 'because'

[Guest]

Test No. incompl/elem-11 "Conditionals", question 2

......... I bought you a new car, would you be very happy?

(a) When
(b) If
(c) As

Test No. incompl/elem-11 "Conditionals", answer 2

If I bought you a new car, would you be very happy?

Correct answer: (b) If
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Which is the diference between when if and as

[Alan]

If introduces a conditional sentence as often means because.
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