B里面的错误不是逗号后面缺主语，but作为并列连词前后主语相同时后面省掉主语是可以的；B的错误在于heard of a instrument，显然听到的应该是一件事而非听到一件器械。

even though, but 赘余。

B heard of an instrument，句意有误。是听说一件事，而非听说一个设备
C 双主语
D 无主句
E though but重复
A correct

B and D - Incorrect because they do not include the "he" in the end. Without this subject, the rest of the sentence doesn't make much sense.

C - Incorrect because the primary clause is just a fragment:
* Remove the parenthetical phrases "even though...telescope", and "in 1609" and you will see that C is missing a verb as it reads: "Gallileo on hearing that such an optical instrument had been made, he quickly built his own"

E - Incorrect because of the double negative "Even though...but when he heard". Double negatives are a no-no on the test.

C, D, and E - Incorrect because "even though" is not appropriate in this case as it isn't consistent with the intended meaning of the sentence. "Even though" should be used to show mitigating circumstances, or to introduce a paradox as in the examples below:

even though...but... 错误！！

B but后边不是完整句子，C句子成分错了，两个主语 D 主句残缺 E无主句

错选b
看后半段可以排除b，when he heard of such an optical instrument having been made, 这里不对
前后都要看用来排除

even though是从属连词，连接的句子做状语从句，but连接两个独立的句子，此处因为even though的存在，前面的句子是状语从句而不是独立的句子，but用法错误。

主句，but 从句， 主句

on hearing一听到，
on hearing, in 1609, that such an optical instrument had been made这句是he quickly built his own device from an organ pipe and spectacle lenses的状语

B和D选项，逗号后面缺少主语，故排除。