【单选题】

Questions 18 to 20 are based on the following passage.At the end of the passage, you will be given 15 seconds to answer the questions. Now, listen to the passage.

What will happen to the workers if the machines are painted gray compared with orangeA．Workers may be more cheerful and energetiC、
B．More errors and accidents will occur.
C．There is no difference at all.
D．They will be more active and curious.