Answer:
the correct answer is el ciclo de vida
Explanation: el ciclo de vida means life cycle so the sentence in english would look like "it is interesting to study the life cycle of butterflies
The correct word to fill the sentence in Spanish, taking into account the context is:
For biologists and other scientists it is very rewarding to study the life cycle of butterflies due to the great diversity of events that it entails.
The butterfly begins as an egg, after which it becomes a caterpillar and begins its feeding process, later it changes to a chrysalis and finally, once it emerges from the pupa, it will be a butterfly as everyone knows it.
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