It depends on where you want to travel to...If you are goin to the UK you can enter with your British Passport. Also you should be fine to travel within the European Union with the same British Passport. Your Green card will give you entrance back into the US when you return.
Only his/her passport is required.
Yes, you always need a passport when you travel outside your country of origin.
Yes, you can. You just have to take your green card along with your Iranian passport.
You can travel within the US with a green card so long as it is valid. A green card is NOT a valid document for international travel outside the US. To travel outside the US, you will need a passport and possibly visas depending upon the passport you hold and the country you visit. Please check with the local embassy/consulate for the most up to date visa requirements for your country's passport prior to travel.
No. NTSA guidelines require a passport (foreign or US), US passport card, green card or US drivers license or non-drivers license.
yes,as long as you have no criminal record.
None - you need a passport. A Green Card is not a substitute for a passport.
Answering "Your passport got lost can you travel with your ID card?"
A Canadian citizen with a green card can use their Canadian passport to exit the US and use their US green card to re-enter the US under the same status. Hope this helps.
A passport from your country of citizenship
No, for international travels, you really need your passport. However, if you plan to land or sea travel to Mexico or Canada and you have your License and your Green Card and Birth Certificate, then you can but you still need the passport when you get back to the US for easier travel.
No, it is not mandatory for green card holders to posses a machine readable passport (as the green card is machine readable).