Answer:
![\huge\boxed{\sf Linking \ Verb}](https://img.qammunity.org/2021/formulas/english/college/3qkdkuc75k5x8umenhotxn53767mdpfheo.png)
Step-by-step explanation:
Donna is my best friend.
Here, Donna is the "subject" while my best friend is "complement of the subject".
Also, "Is" is acting as a linking verb here as it is "linking" the subject and subject complement.
![\rule[225]{225}{2}](https://img.qammunity.org/2021/formulas/chemistry/middle-school/ri1osubq0ul0fyszs3s2hvchlv85n22xxb.png)
~AnonymousHelper1807