Explanation
These are the mechanisms that the Salesforce REST API uses for authentication. According to the Salesforce documentation1, the REST API requires an access token obtained by authentication. The access token is a session credential that represents the authorization of a specific application to access specific parts of a user's data2. The access token is valid for a limited time and can be refreshed using a refresh token. A refresh token is a credential that represents the authorization of an application to refresh an expired access token2.
Option A is incorrect because an authentication token is not used by the Salesforce REST API. An authentication token is an email security feature that appends a unique string of characters to your password when you log in from an unrecognized device or IP address3. Option B is incorrect because a session ID is not used by the Salesforce REST API. A session ID is a unique identifier for a user's session that can be used for SOAP API calls4.
References: 1: Step Two: Set Up Authentication | REST API Developer Guide | Salesforce Developers 2: Use Salesforce REST APIs with Heroku - Trailhead 3: Authentication Token - Salesforce 4: Session ID - Salesforce

Explanation
To allow users to login with their Facebook or LinkedIn credentials, Salesforce will play the role of a service provider (SP). A SP is an entity that relies on an identity provider (IdP) to authenticate and authorize users. In this scenario, Facebook and LinkedIn are the IdPs, and Salesforce is the SP. The SP receives a token from the IdP and uses it to access Salesforce resources. The other options are not correct for this scenario. References:
Service Provider, Social Sign-On with Authentication Providers

Explanation
Using the App Launcher with SSO and using a connected app are two features that can be utilized to provide users with login and identity services for the third-party application. The App Launcher allows users to access multiple apps from one location with SSO. The connected app allows users to authorize access to the third-party application using OAuth 2.0. The other options are either not relevant or not applicable for this use case. References: App Launcher, Connected Apps