Sentence improvement — Correct tense with a definite past-time marker: improve ‘‘Other countries have eradicated this disease ten years ago.’’ by selecting the appropriate simple past form for a time-adverbial ‘‘... years ago’’.

Given dataOther countries have eradicated this disease ten years ago.

Concept/ApproachWith a specific past time (‘‘ten years ago’’), English requires the simple past, not the present perfect.

Step-by-step evaluationeradicated — Correct simple past: ‘‘... eradicated this disease ten years ago.’’had eradicated — Past perfect needs a second, later past reference; not present.did eradicated — Incorrect auxiliary + past form combination; should be ‘‘did eradicate’’ if emphasis were needed.No improvement — Keeps wrong tense.

Verification/AlternativeRule of thumb: ‘‘ago’’ → simple past.

Common pitfallsOverextending present perfect with explicit past-time adverbials.

Final Answereradicated