Detect the erroneous segment; if none, choose ‘‘No error.’’ Sentence: I have had to work at the fountain for almost ten hours before it could start functioning well.

Introduction / Context:
This question checks prepositional choice with the verb ‘‘work’’ when the meaning is ‘‘repair/operate on a device’’ rather than ‘‘work at a location.’’

Given Data / Assumptions:

• Intended sense: The speaker spent time repairing/setting right a machine (‘‘fountain’’).
• With ‘‘work’’ + object meaning ‘‘make operational,’’ the idiomatic preposition is ‘‘on’’ (work on a machine).

Concept / Approach:
‘‘Work at’’ typically marks a place of employment or general activity at a site. ‘‘Work on’’ marks the object of repair/improvement.

Step-by-Step Solution:
Identify sense: repair/bring to working order.Replace preposition: ‘‘at’’ → ‘‘on’’.Corrected sentence: ‘‘I have had to work on the fountain for almost ten hours before it could start functioning well.’’

Verification / Alternative check:
Parallel: ‘‘work on the engine/computer/elevator,’’ not ‘‘work at the engine.’’

Why Other Options Are Wrong:

• A: Perfect present construction is fine.
• C–D: Time and result clauses are grammatical.

Common Pitfalls:
Using ‘‘at’’ by default with any noun after ‘‘work’’ irrespective of meaning.

Final Answer:
at the fountain for almost