Riley and aaron are in an orchestra. riley plays the flute and aaron plays the oboe. to warm up, they play the same note at the same loudness, pitch, and duration. yet the audience can still distinguish between the two, due to the difference in

   Timbre

Explanation:  Timbre in the general sense means something that is originally recognisable by someone or something, that is, a recognisable character. In the musical sense, timbre means a recognisable character, a musical characteristic of an instrument, a recognisable voice or sound. Timbre, therefore, does not depend on the note or duration, loudness, pitch, etc., because each instrument has its own typical sound. So even though two musicians play two different instruments with the same pitch, duration, etc., it can always be distinguished which instrument is in question because each one is based on a specific sound, i.e. timbre.

even though you have attached neither the chart nor the generalizations, i have located them online. the right answer is d, since they are asking you about a generalization. you can only infer from the chart that between 2008 and 2009 the number of employed workers decreased significantly (from over 115 millions to 107 millions approximately), which signals some type of economic crisis.