Read this excerpt from Robert Stawell Ball’s Great Astronomers:

Though every child may now know more of the actual truths of the celestial motions than ever Ptolemy knew, yet the fact that his work exercised such an astonishing effect on the human intellect for some sixty generations, shows that it must have been an extraordinary production. We must look into the career of this wonderful man to discover wherein lay the secret of that marvellous success which made him the unchallenged instructor of the human race for such a protracted period.

Based on the context of the excerpt, what does the word protracted most clearly mean?

seeming to be truthful

weighing an excessive amount

extending in a specific direction

continuing for a long time

being exceptional or talented

When we do not know the meaning of a certain word, we can try to guess it by analyzing the context in which it is inserted. In this particular case, the word "protracted" accompanies "period". The speaker had already revealed previously that Ptolemy's work influenced sixty generations, which means his work was important and influential for a very long period of time. Thus, when the speaker continues and restates that Ptolemy was a success and the "unchallenged instructor of the human race for such a protracted period," we already know that he means Ptolemy was a success for a very long time. Thus, the best assumption would be letter D) continuing for a long time.

As a matter of fact, protracted is an adjective that refers to something that lasts for a long time or, at least, longer than expected.