Explanations:The past continuous tense is used to describe actions that were ongoing at a specific time in the past. It is formed using the auxiliary verb "was" (for singular subjects) or "were" (for plural subjects) followed by the present participle of the main verb (verb + -ing). This tense is often used to set the scene or background for another action that occurred in the past, or to describe an action that was in progress when another action occurred.
Let's break down the structure of the past continuous tense:
1. **Auxiliary Verb**: The auxiliary verb used in the past continuous tense is "was" for singular subjects (I, he, she, it) and "were" for plural subjects (we, you, they).
2. **Present Participle**: The main verb is transformed into its present participle form by adding "-ing" to the base form of the verb. For example, "read" becomes "reading", "walk" becomes "walking", and "run" becomes "running".
3. **Time Reference**: The past continuous tense often includes a time reference that indicates when the action was taking place. This can be a specific time (e.g., "at 3 o'clock"), a time expression (e.g., "yesterday"), or another action that occurred at the same time (e.g., "when she called").
Now, let's examine the options provided:
**Option A: "I have been reading."**
This sentence uses the present perfect continuous tense, which is formed with "have/has been + verb-ing". It describes an action that started in the past and continues up to the present. For example, "I have been reading this book for three hours." This tense is not the past continuous tense.
**Option B: "I read the book."**
This sentence uses the simple past tense, which is formed with the base form of the verb. It describes a completed action in the past. For example, "I read the book last night." This tense is not the past continuous tense.
**Option C: "I was reading when she called."**
This sentence correctly uses the past continuous tense. It describes an ongoing action ("was reading") that was happening when another action occurred ("when she called"). This is the correct form of the past continuous tense.
**Option D: "I will read tomorrow."**
This sentence uses the future tense, which is formed with "will + base form of the verb". It describes an action that will happen in the future. For example, "I will read the book tomorrow." This tense is not the past continuous tense.
In summary, the past continuous tense is used to describe ongoing actions in the past, and it is formed with "was/were + verb-ing". The correct option in this case is "I was reading when she called" because it correctly uses the past continuous tense to describe an ongoing action in the past.