Respuesta :
The answer is: D. continuing for a long time.
The adjective protracted means lasting for a long time or for a longer time than expected or usual.
In the excerpt from "Great Astronomers," by Irish astronomer Robert Stawell Ball, the speaker makes reference to Greek astronomer Claudius Ptolemy's and his legacy. Ptolemy was born around the year 85 A. D. As a consequence, the author acknowledges how Ptolemy's studies have influenced humanity for "sixty generations."