nous évitera

Question

I do not understand the last sentence.  Why use the third person singular with "nous"?  Or should this be "on" not "nous"?

Maarten Kamp · Accepted Answer

Patricia, 
this is a pretty complex sentence in French (especially at B1 level, I think ).
The ‘simple’ answer to your question is that it is the infinitive ‘ marcher ‘, used as a noun, that is the subject of éviter in this sentence. 
When used as nouns, infinitives follow 3rd person singular conjugations, giving the future tense of the verb éviter as ‘évitera’ in the sentence.
The sentence is complex because there are 2 verbal expressions following the subject, the latter including a pronominal verb : 
1. “ éviter à qqn de faire qqc “ ( à qqn giving rise to the indirect object pronoun ‘ nous ‘  preceding the verb ' éviter ' in this phrase, and ' nous ' cannot be replaced by the subject pronoun ‘ on ‘ ) 
and with ‘ faire qqc ‘ replaced by 
2. ‘ se tromper de qqc ‘ ( another fixed expression ), with ' nous ' in this expression being the pronominal pronoun
 https://progress.lawlessfrench.com/revision/glossary/verbal/infinitif-infinitive 
https://www.thoughtco.com/french-infinitive-linfinitif-1368866 
https://www.lawlessfrench.com/grammar/infinitive/
https://www.wordreference.com/fren/%C3%A9viter 
 https://www.wordreference.com/fren/se%20tromper%20de

Céline Pickard · Answer

Bonjour Patricia,
Maarten is correct. Take a look at the examples below:
Faire du sport est bon pour la santé. = Doing exercises is good for your health.
Nager devrait t'aider à muscler ton dos. = Swimming should help you muscle your back.
Parler le français t'aidera à mieux communiquer avec tes amis français. = Speaking French will help you better communicate with your French friends.
You might also want to take a look at the lesson link below:
https://french.kwiziq.com/revision/grammar/how-to-translate-the-ing-form-of-the-verb-by-the-infinitive-and-not-by-ant
I hope this is helpful.
Bonne journée !

Giovanna Becattini · Answer

parce que « marcher » est le sujet et « nous » est le complément d'objet