A speaker's credibility is MOST clearly determined by the audience's perception of



posture and stance
vocal pitch and volume
cleanliness and neatness
competence and character

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.  

answer; exploratory;