I don't know what "Track" means in this sentence
I've look it up in a bilingual dictionary and in a english english dictionary but I think I didn't find the meaning I was waiting for "keeping track of several ideas at the same time"

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Another way to say this would be:  Keeping separated several ideas at the same time without confusion.

Track is like what a train is on.  it is separate from other tracks going in the same direction.  The tracks never cross or meet (or get confused with each other.)  The separation is important for safety in a train track.  So this is why track means in line continuously in an organized way.

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In my opinion,"trace" in this sentence means that you hesitate to make a decision between those ideas,you don't know how to choose.

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As far as I know, "keep track" here means to follow, to watch, to trace.