DNA is one of the most important discoveries in science. DNA is the plan for the human being, as a blueprint is the plan for a building. DNA makes a person look the way he does. A person's DNA comes from a mixing of his parents' DNA. That's why a child looks like his parents. But, besides controlling things such as height and hair color, DNA can also give people diseases. Scientists are now studying DNA to cure diseases. In the seventies, scientists developed a process called recombinant or RDNA. Although it sounds difficult to understand, RDNA simply means taking DNA from one animal or plant and putting it into another. By doing so, scientists can create new beings. In doing so, scientists can better understand DNA, especially what parts of DNA do what. After they understand DNA, scientists can begin to cure diseases. Often, the new being created will itself be the cure.   Besides curing diseases, RDNA research can also do other things. For example, scientists in Japan have already created "super-trees". Trees help humans, because they take CO2, which poisons humans, from the air and turns it into oxygen, which lets humans breathe. "Super-trees" do this too, but do it much faster. As things such as cars and factories have already put much CO2in the area, "super-trees" are badly needed. Unfortunately, there is a serious danger in RDNA research. Scientists want to create animals to cure old diseases, but these new animals may also create new diseases. It will be a serious problem if the animals escape from the science laboratory and into nature. As these animals are not natural, they may _ many new powerful diseases. As a result, RDNA research will create many solutions, but it will also create many problems. From the passage, we can know that a boy looks like his parents because  _  .
he is son of his parents. his parents' DNA decides his appearance. he has received DNA from his father or his mother. scientists have put some of his parents' DNA into him.