Hello. I would like to brink my parents to US for a visit, but i don't know exactly how to complete the DS-156...for example, my parents don't have a fax no...so should i leave the space blak, or write NONE, or N/A? Pls anybody...this is confusing. They've never been in America, so to that question i select NO button, but then they ask about what type of visa they came here with

...should i write N/A?
Do this things actualy matter that much? If i leave blank space there where there is absolutly nothing to fill...would that be a problem?
Also, because i am a LPR and my husband is USC, he will complete Affidavit of Support. Does it matter?
thank you for any sugestions