“Researchers are finding harmful effects at lower levels of exposure.” How can this line be interpreted?

(A) As Maria returned home,/ (B) she found the hall to be empty as/ (C) everyone were hiding in the kitchen./ (D) No error 

Environmental toxins which can affect children are frighteningly commonplace. Besides lead, there are other heavy metals such as mercury, which is found frequently in fish, that are spewed into the air from coal-fired power plants, says Maureen Swanson, MPA, director of the Healthy Children Project at the Learning Disabilities Association of America.

Mercury exposure can impair children‘s memory, attention, and language abilities and interfere with fine motor and visual-spatial skills. A recent study of school districts in Texas showed significantly higher levels of autism in areas with elevated levels of mercury in the environment. “Researchers are finding harmful effects at lower and lower levels of exposure,” says Swanson. “They‘re now telling us that they don‘t know if there‘s a level of mercury that‘s safe.”

Unfortunately, some of these chemicals make good flame retardants and have been widely used in everything from upholstery to televisions to children‘s clothing. Studies have found them in high levels in household dust, as well as in breast milk. Two categories of these flame retardants have been banned in Europe and are starting to be banned by different states in the United States.

(A) As Maria returned home,/ (B) she found the hall to be empty as/ (C) everyone were hiding in the kitchen./ (D) No error

The number of toxins in our environment that can affect children may seem overwhelming at times. On at least some fronts, however, there is progress in making the world a cleaner place for kids and just possibly, reducing the number of learning disabilities and neurological problems. With a number of efforts to clean up the environment stalled at the federal level, many state governments are starting to lead the way. And rather than tackle one chemical at a time, at least eight states are considering plans for comprehensive chemical reform bills, which would take toxic chemicals off the market.

Question

(A) As Maria returned home,/ (B) she found the hall to be empty as/ (C) everyone were hiding in the kitchen./ (D) No error

“Researchers are finding harmful effects at lower levels of exposure.” How can this line be interpreted?

(A) As Maria returned home,/ (B) she found the hall to be empty as/ (C) everyone were hiding in the kitchen./ (D) No error