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consider these sentences:

i have a new hobby.

i keep track of all the wild birds i spot.

which sentence uses parenthetical elements most effectively to combine the information in the sentences?

i have a new hobby, which is keeping track of all the wild birds i spot.

i have a (new) hobby, which is keeping track—of all the (wild) birds i spot.

i have a new hobby, keeping track—of all the wild birds i spot.

i have a new hobby—keeping track—of all the (wild) birds (i spot).