After reading the sentence and the options, we can complete it with letter B in the following manner:
"While I was watching the performance, I met one of my old friends."
To answer this question, first let's look at the sentence. Its second part uses a verb in the simple past (met). Therefore, we can assume the first part will also refer to an action that happened in the past.
With the information above in mind, we can already eliminate letters C and D, since they use the simple present and the present continuous.
Now, at the beginning of the sentence, we see the word "while". "While" is normally used with continuous tenses to indicate an action in progress, either in the past or in the present.
Because of the use of "while", we can conclude that the best option among the two remaining is letter B. "Was watching" is in the past continuous, indicating an action that was in progress when another action happened.
Therefore, the best way to complete the sentence is: "While I was watching the performance, I met one of my old friends."
Learn more about the past continuous tense here:
https://brainly.com/question/14025107
