天山 4
Q 17:
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.
A. Galileo did not invent the telescope, but on hearing, in 1609, that such an optical instrument had been made, he
B. Galileo had not invented the telescope, but when he heard, in 1609, of such an optical instrument having been made,
C. Galileo, even though he had not invented the telescope, on hearing, in 1609, that such an optical instrument had been made, he
D. Even though Galileo did not invent the telescope, on hearing, in 1609, that such an optical instrument had been made,
E. Even though Galileo did not invent the telescope, but when he heard, 1609, of such an optical instrument being made, he
ANS A
请指教 why not B or C?
还有, “on hearing”如何解?
Thanks. | 
