Rosalind Wants to Add Attribute Declarations to Her DTD, and She

Rosalind wants to add attribute declarations to her DTD, and she turns to you for information about the possible attribute types.
-You help Rosalind write the declaration of the "semester" attribute described in the previous problem.Which of the following is an appropriate declaration for this attribute?

A) <!ATTLIST course semester (fall | spring | summer) #REQUIRED>
B) <!ATTLIST course semester (fall, spring, summer) #REQUIRED>
C) <!ATTLIST semester course (fall | spring | summer) #REQUIRED>
D) <!ATTLIST semester course (fall, spring, summer) #REQUIRED>