67. According to the passage, which of the following statements is true? 8 (A) Parents should listen to doctors with patience instead of giving a flat refusal to vaccination. (B) Child developmental impairments are proved to be the result of vaccination. (C) Nowadays, lots of children who do not receive vaccines are infected with diseases such as polio or smallpox. (D) The risk of having vaccine side effects is so high that many parents object to the vaccination.