Error Spotting – Choose the part (A–D) that contains a grammatical error, or choose No error if the sentence is fully correct. Sentence (parts correspond to options below): A) I was standing B) at the bus stop C) waiting for him D) since eight o'clock.

Introduction / Context:
This sentence checks correct tense choice with the preposition since, which marks a starting point in time and typically pairs with perfect or perfect progressive aspect, not a simple past progressive that does not cover the entire interval up to a reference point.

Given Data / Assumptions:

• Temporal marker: since eight o'clock
• Verb phrase provided: was standing (past progressive)
• Implied context: ongoing action from 8:00 to a later point

Concept / Approach:
Use have/has been + present participle for a current reference period, or had been + present participle for a past reference period. Since introduces the start time; the perfect progressive expresses duration from that start to a reference point.

Step-by-Step Solution:

Verification / Alternative check:
Paraphrase using for: I have been standing for two hours. This shows that the action continued from the start time to the reference time, something the past progressive alone does not convey with since.

Why Other Options Are Wrong:

• B) Location phrase is fine.
• C) Present participle clause is fine.
• D) The preposition since is correct; the mismatch lies in the verb aspect earlier in the sentence.

Common Pitfalls:
Learners often try to pair since with simple or past progressive forms. Remember that since introduces a starting point that calls for perfect aspect to express duration.

Final Answer:
Option A contains the error. Use have been standing or had been standing depending on context.