Which word in this sentence is a coordinating conjunction?
i took the book back to the library, for the book had a few pages missing.
a back
b to
c had
d for

answer: i would say he was very determined and persistent in overcoming obstacles.

explanation:   "the magician of menlo park" as he was called, liked to tell an incident that happened when he was 8 years old and came back home crying after attending school for three months because his teacher called him "sterile and unproductive". from nowadays perspective, we can say that thomas alva edison was one of the most persistent and determined man that has ever existed. when edison was 14, he contracted scarlet fever. the effect of the fever, as well as a blow to the head by an angry train conductor, caused edison to become completely deaf in his left ear, and 80-percent deaf in the other. so as you can see he had to struggle to not so many minor issues but he always succeeded.

i would have to say "a" or "d".