I would be highly grateful......

[Banglardon]

In a formal letter, when making a polite request can I use the following three sentences interchangeably?

1- If you will be attending the site visit, I would be grateful if you could complete the tear-off slip below.
2- If you will be attending the site visit, I would be grateful if you would complete the tear-off slip below.
3- If you will be attending the site visit, I would be grateful if you completed the tear-off slip below.

 

[jutfrank]

Don't ask whether they're interchangeable or not. That isn't the right question.

What you're doing here is politely requesting that someone do something. Use 2. You don't need to worry about the others.

I would be grateful if you would + infinitive verb