Read each sentence to find out whether there is any grammatical or idiomatic error in it. The error, if any, will be in one part of the sentence. The corresponding letter of that part is the answer. If the given sentence is correct as it is, then choose option ‘No error’ as your answer response. (Ignore errors of punctuation, if any).

The old tree in the (A)/ backyard was slowly died, its (B)/ leaves turning brown (C)/ and branches becoming brittle. (D)

Correct option is B

Part (B) contains an error. The phrase "was slowly died" is incorrect. The correct form should be "was slowly dying" because "was" is used with the present participle to form the past continuous tense, indicating an ongoing action in the past.
The correct sentence should be: "The old tree in the backyard was slowly dying, its leaves turning brown and branches becoming brittle."
Rule: Use the past continuous tense (was/were + present participle) to describe an action that was ongoing in the past. Here, "was slowly dying" is the correct form.