GMAT Sentence Correction (SC) | Re: Galileo did not invent the telescope, but on hearing, in 1609, that su

Hiall.

Galileo did not invent the telescope, but on hearing, in 1609, that such an optical instrument had been made, he quickly built his own device from an organ pipe and spectacle lenses.

Since it is not difficult to understand the meaning of this sentence, let’s quickly get into theerror analysis:

1.Use of past perfect tense is correct because 1609, the telescope had been already made and after that Galileo made his own version of the instrument. So there are two past events and “had