Select the option that expresses the given sentence in active voice.
"I am upset because my cell phone has been stolen."

Converting Passive to Active Voice:
· Passive: "My cell phone has been stolen."
· Active: "Someone has stolen my cell phone."
Explanation:
1. The agent (doer of action) in a passive sentence is often unknown. In this case, we use "someone" in the active sentence.
2. The verb "has been stolen" (passive) changes to "has stolen" (active).
3. The object "my cell phone" remains unchanged.
Other options:
· (a) "I was upset..." → Incorrect tense shift; the original sentence is in present tense.
· (c) "has been stealing..." → Incorrect because the original sentence implies a completed action, not a continuous one.
· (d) "I have been upset..." → Incorrect because it unnecessarily changes the sentence structure and meaning.
Thus, the correct answer is (b) "I am upset because someone has stolen my cell phone."