What are the differences between the invited and uninvited application letters in their opening part? ( )
选项：

A:You should be specific about the position in an invited letter while just state your desired position or relevant departments in an uninvited letter.
B:You are expected to tell readers how you learned about the organization or the position in an invited letter which is unnecessary in an uninvited letter since it is not written in response to any job advertisement.
C:You should state your purpose clearly in an invited application letter but not in an uninvited one.
D:You can tell the reader why you are making the inquiry in an uninvited application letter but not in an invited one.