A Comprehensive Grammar of the English Language란 책(Randolph Quirk, Sidney Greenbaum, Geoffrey Leech, Jan Svartvik 저)에 답이 나와 있네요~ 토익 만점자이시니 제가 본문을 그대로 인용해드릴테니 한번 읽어보세요.

* Subornidators for -ed clauses and verbless clauses

Clauses with an -ed participle and verbless clauses may be introduced by some subordinators that are also used for finite clauses:

as soon as, although, as if, even if, if, once, though, unless 등

These clauses can be related to finite clauses for which the subject and the verb BE are supplied.

The subject of the subordinate clause must generally be understood as identical with that of the matrix clause, but for verbless clauses such as 'if necessary' and 'where possible' it may refer to the matrix clause as a whole.

=> As soon as 뒤에는 과거분사구문이나 동사가 없는 구문이 올 수 있음을 알 수 있습니다. 

* Subordinators for -ing clauses

Clauses with an -ing participle may be introduced by any of the subordinators for -ed participle clauses, except that the subordinators where, wherever, as, and as soon as are excluded:

although, as if, as though 등~

=> 맨 마지막 문장 보시면 as soon as는 현재분사구문이 뒤에 올 수 없음을 알 수 있습니다.

 그렇기 때문에 As soon as discovering the error ~~ 이 문장은 틀린 문장임을 알 수 있습니다. ^^

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