Suppose that a cereal manufacturer tried out a new cereal box design for a few months, andduring the ...

Suppose that a cereal manufacturer tried out a new cereal box design for a few months, andduring the same time periodnotices that its sales have tripled. One of the cereal executives, Mr. Correl, boasts that the new cereal box must have sparked the increase in sales. But another executive, Mr. Scien, points out that the increase could be due to the new advertising campaign that the company is using, or to new distribution practices that have taken hold, or to the fact that more and more people are eating cereal these days. That is, Mr. Scien suggests that the company's test of the new cereal box design is low in ____.
 
  a. operationalizing
  b. generalizability
  c. internal validity
  d. external validity