Childhood exposure to a group of chemicals, which are used widely in a variety of products, including water-resistant clothing and microwave popcorn, could reduce the effectiveness of common vaccines, a new study has found. Researchers at the Harvard School of Public Health in Boston looked at over 580 children and found that those who had higher concentrations of these perfluorinated(全氟化的)compounds(PFCs)in their blood had lower immune responses to diphtheria(白喉)and tetanus(破伤风)vaccinations. An insufficient immune response to a vaccine can mean a child is actually vulnerable to catching a disease even though they have been vaccinated against it, the researchers said. " When we take our kids to the doctor's office to get their shots, we expect that the vaccines are going to work. What we found was that there was an increasing risk that they didn't work if the kids had been exposed to the PFCs," study author Philippe Grand-jean was quoted as saying by Live Science.

单选题 What makes the children's common vaccines less effective according to the new study?

A、 The exposure of chemicals they used in childhood.
B、 The reduction of a series of chemicals in childhood.
C、 Childhood consumption of chemical products.
D、 Childhood contact with chemical products.

【正确答案】 D

【答案解析】解析：细节题。根据关键词the children’s common vaccines less effective定位于首段，儿童跟化学物品接触会降低常见疫苗的有效性。故选D。

单选题 The Harvard School of Public Health experts found that there was ______ relation between concentrations of chemical deposits in blood and immunity.

【正确答案】 C

【答案解析】解析：根据关键词定位于第二段， “found that those who had higher concentrations of these perfluorinated…”有一定的关系，C项比较符合题意，故选C。

单选题 The word "vulnerable"(Para. 3)is closest in meaning to "______".

单选题 The increasing risk of low immunity which children face is caused by______.

【正确答案】 A

【答案解析】解析：细节题。根据关键词定位于最后一段的最后一句What we found was that there was an increasing risk that they didn’t work if the kids had been exposed to the PFCs。A项比较符合题意，故选A。