The European parliament
A)
Elected representatives are representatives who have been elected for their job. In some cases, a countries government could send an MP to a meeting in Europe but they would not have been elected to go, they would have selected. An elected representative will have been chosen by a vote either from a vote in a parliament or a public vote to go to the EU commission and represent their countries interests.
The benefit of an elected representative would hopefully that they try to do more to please their countries although this can have the side effect that they will not support a ruling that will not please their voters and so this can make it hard to get anything done in the EU commission because everyone has their own agenda. Someone who was appointed might be able to work together with the other EU representatives and get things done much easier.