Is the verb "is" a LINKING VERB or ACTION VERB? Donna is my best friend.

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.

i decided to stay late in the laboratory to continue my experiment with the lightbulb. at midnight, thomas edison opened the door and saw all the stuff he was working on. the lightbulb, film and the transmitter. as he walks in an idea hits him on how the lightbulb would work. he would have to change a few wires around to get it to light up. when he did change the wires around it worked so he decided to write a telegraph to his friend to tell him about his success.   as he was packing up he grabbed the telegraph and walked to his home. he told his wife about the success and the next morning mailed the telegraph.