Question

he failed to my great surprise. turn into complex​

Answer 1

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==> He was failed by my great surprise .

Answer 2

$\small\mathcal\red{Simple\:sentence}$

He failed to my great surprise.

$\small\mathcal\red{Complex\:sentence}$

He was failed by my great surprise .

$\sf\pink{Complex\:sentence\:Defination\:\:-}$

A complex sentence is a sentence that contains one independent and one dependent clause.