"I highlighted the changes in yellow." Is it grammatically correct?
I sent a email and I'm not sure if it's correct.
Thank you in advanced.

Question

Answer

Yep, it's a very common phrase in U.S. schools and offices.  By the way, why does your profile say that your English level is "native"?

Answer

Yes. Perfect!

Answer

I sent an email. 
Are you learning Spanish? If so, I highly recommend you to watch this video https://www.youtube.com/watch?v=v30Za-XLdTg&feature=youtu.be

Answer

I sent an email. 
Are you learning Spanish? I highly recommend you to watch this video. It might be helpful for you.
https://www.youtube.com/watch?v=v30Za-XLdTg&feature=youtu.be

Answer

Yes, that is correct.  But:

I sent aN email and I'm not sure if it's correct.
Thank you in ADVANCE.

Ne manquez pas cette occasion d'apprendre une langue depuis chez vous. Découvrez notre sélection de professeurs de langues expérimentés et inscrivez-vous dès maintenant à votre premier cours !