Questions 4 to 7 are based on the following conversation. At the end of the conversation, you will be given 20 seconds to answer the questions. Now listen to the conversation. In general, about_____ of complaints cannot be investigated.

A．Language acquisition may be negatively affected.
B．Babies used in experiments often develop emotional problems.
C．Parents may force their children to learn at too early an age.
D．Early coaching will interfere with creativity.

A．Yellow and red.
B．Dark yellow.
C．Light yellow.
D．Bright yellow.