French language Q&A Forum

My question was asked below, but the answers provided did not address my confusion. 
One example given in this lesson is "Si nous l'avions choisi, nous l'aurions regretté".

A previous lesson on 'if-then" sentences (Imperfect usage - hypothesis | French Grammar | Progress with Lawless French) says the following: 
 "You can never use Le Passé Composé nor other past tenses in this context."
I took this to mean that all if-then sentences must use an "imparfait + conditionel présent" form. 

But here we are using the plus-que-parfait and the conditional passé in an if-then sentence. There is no mention of the plus-que-parfait + conditional passé form in the lesson linked to above.

Can you please clarify the rules around using plus-que-parfait + conditional present in 'if-then' sentences? 

Thanks.

Why do we use the verb "rencontrer" instead of "retrouver". They already know each other. 

In a recent Kwizbot about the article with days of the week/weekend, an example was given « Ce weekend, on est allés au Futuroscope ». Why is the past particle plural?  « We » is implied but the subject is « on ».

I will be well rested Kwizbot answer: " je serai bien reposé."

I translated as: "je me serai bien reposé."

Pose TOUT sur la table. Why not use TOUS as there are more than one item to put on the table. Merci, Diana

In reference to the rule which is explained at the end of the lesson after the examples, isn't there something extra going on in the reflexive verbs which follow the pattern of eler/ eter like 'se rappeler'? For example, we have je me rappelle in the present, but je me rappelais in the imperfect, so we don't just add 'ais' to the stem of the conjugation in the present in this instance, right? 

As an American, I'm noticing that using "wash" as a transitive verb is tripping me up a little. It sounds ungrammatical to me ear to use it transitively. I'm guessing this could be a difference between American and British English, maybe (if a British speaker says it sounds fine).

I can say, "I wash up every morning" or "I'm wash myself every morning," but "I wash every morning" doesn't say what I'm washing, so it sounds like an incomplete sentence.

Reading the Kwiziq lessons has been great. They're both thorough and concise, which is impressive. Thanks!

My answer was "Celui-ci ou celui-là". I'm perplexed as to why this cannot be a correct form.