Inversion used in conditionals

[Mefodij]

English Language Tests, Intermediate level

ESL/EFL Test #120 "Conditional Tenses", question 7

......... he been more careful, he would have spotted the mistake.

(a) Were
(b) Had
(c) Has
(d) Is

English Language Tests, Intermediate level

ESL/EFL Test #120 "Conditional Tenses", answer 7

Had he been more careful, he would have spotted the mistake.

Correct answer: (b) Had
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What is the grammar structure in this question?
I've never seen such a structure.

Mefodij

[Alan]

Hi Mefodij,

This inversion is used in a conditional sentence. We say: Had I been more careful ... which means the same as: If I had been more careful ...
Alan
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English as a Second Language
You can read my ESL story Present Simple