I ———————– (read) when...
The sentence describes an action that was ongoing in the past when another event occurred. The correct tense to use here is the Past Continuous Tense, which is formed using "was/were" + present participle (verb+ing). Therefore, "I was reading when the lights went out" is the correct usage.
View all questions of this testI ———————– (read) when...
Since the verb is read, all you have to do is find the right tense in this question. "The lights went out" indicates that you need to use it in the past tense. Without the use of a support word, in the case of "was done reading" ("done" is the support word), we can't keep the sentence grammatically correct. So we're only left with the past continuous form, 'was reading'.
I ———————– (read) when...
Have been read