Which of these is NOT true about external objects?

An app builder has been asked to provide users a way to identify a Contact's "Preferred Contact Method" direction on Contact record. Users need to be able to identify whether a phone number or an email, is the Contact's preferred communication method. Which filed type will allow the App Builder to accomplish this with the fewest fields possible?

The app builder at Ursa Major Solar has just created a master-detail relationship between a parent object Galaxy__c and child object Star__c.
What would be the effect of creating this type of relationship if users want to report on Galaxy__c with Star__c?

An app builder has been asked to integrate Salesforce with an external web service. The web service must be notified every time an opportunity is won.
What are two ways to satisfy this requirement? (Choose two.)

The CFO wants to make sure that a deal with more than a 40% discount gets approved by the VP of Finance before a quote is sent to the customer.
In which two ways can this be accomplished? (Choose two.)