French language Q&A Forum

I found that the sound quality on this recording was really terrible, there's an echo that made it really difficult to make out what the speaker was saying, so I abandoned it.

Line 11: on which professionals or amateurs can buy or sell.....

is being corrected to:

sur laquelle professionnels et amateurs peuvent acheter ou vendre........

Hi, I am just wondering if in the following sentences, we could use " l'on" instead of "on" - as per 

https://www.lawlessfrench.com/grammar/on-vs-lon/

(L') On passe toujours La Saint Sylvestre entre potes.

(L') On allume la télé pour voir le feu d'artifice de la tour Eiffel,

Et puis, le lendemain matin, comme (l') on aura tous la gueule de bois (comme d'habitude)

(l') on remplira nos flûtes d'Efferalgan et (l') on criera 'Santé!' en rigolant.

I get really confused with knowing when to use expressions such as "à laquelle". I've read the lesson however for this text for example, why can't I use "que" as well as "à laquelle" for - 'une surprise à laquelle je ne m'attendais pas du tout' ?