Answer:
1. If you happened to go to the shops, could you buy me some toothpaste?
2. They'll return his money as long as he has the original receipt.
3. We won't be able to go to Paris unless we have enough money.
4. If only we had gone to the party yesterday.
5. You'll be able to contact her any time in case you need her help.
Explanation:
1. If you happened to go to the shops, could you buy me some toothpaste?
In this sentence, "happened" is used to mean the same intention of asking for help.
2. They'll return his money as long as he has the original receipt.
The use of the phrase "as long as" presents a valid reason for why or how the refund will be given, which is the same as "but only if".
3. We won't be able to go to Paris unless we have enough money.
"Unless" is and can be used to mean the same as "if" for it presents a condition for a successful 'action/result'.
4. If only we had gone to the party yesterday.
Using "if only" in the sentence presents the same feeling of regret in "what a shame".
5. You'll be able to contact her any time in case you need her help.
The use of the phrase "in case" presents the same intention of a need and replaced the word "because".
