A single night of taking the drug Ecstasy (摇头丸) can cause serious brain damage and speed up the start of Parkinson’s disease（帕金森综合症）, scientists say. Just two or three Ecstasy tablets can permanently destroy brain cells that affect movement and reasoning, according to American research that links the drug to Parkinson’s for the first time.
A study by a team at Johns Hopkins University in Baltimore, Maryland, involving squirrel monkeys and baboons (狒狒) found that both species suffered permanent damage to key cells, which are lost in Parkinson’s, after receiving three low doses（剂量）of Ecstasy at three-hour periods.
The study is particularly important because baboons are one of the best animal models for the human brain. George Ricaurte, who led the research, said that the widespread abuse of drug might have caused severe damage. “The most troubling result is that young adults using Ecstasy may be increasing their risk of developing Parkinsonism as they get older.”
Alan Leshner, a former director of the US National Institute on Drug Abuse, said, “This study emphasizes the multi-aspect damage that Ecstasy causes to users. We’ve long known that repeated use damages brain cells. But this study shows that even very occasional（偶尔） use can have long-lasting effects on many different brain systems. It sends an important message to young people: don’t experiment with your own brain.”
Janet Betts, a mother whose teenage daughter Leah died after a single Ecstasy tablet in 1995, said, “This comes as no surprise. But people can’t see the effects at first, and they say it won’t happen to them. We’ll see the symptoms later, just as we have with smoking.”
The article is intended to ______.

A．explain the bad effects of drugs on people’s health

B．warn young people of the risk of taking the drug Ecstasy

C．persuade people out of such bad habits as smoking and using drugs

D．tell us the links between the drug Ecstasy and the animal models

We know from the passage that a low dose of Ecstasy ______.

A．can permanently destroy one’s brain cells

B．can cause serious brain damage occasionally

C．will result in immediate symptoms

D．may bring on Parkinson’s at once

Why are squirrel monkeys and baboons involved in the experiments?

A．Because these animals usually take drugs.

B．Because their brain is similar to human beings.

C．Because there is a model in the animals’ brains.

D．Because they will soon get well after the experiment.

The underlined word “it” in the last paragraph probably refers to”        ”.

A．Leah’s death after a single tablet

B．the symptoms after smoking

C．the damage to the brain systems

D．repeated use of the drug