.关于声音的发生，下列说法中正确的是

A．振动的物体都能够发出声音

B．我们听到的声音一定是由物体的振动产生的

C．振动慢的物体不能发声，振动快的物体能发声

D．因物体的材料、结构不同，所以有的物体振动时能发声，有的物体振动时不能发声

Today, we’ll talk about what other effects watching TV might produce on children. Children should be (1) a lot of television, many experts and parents agree, but there is at least one circumstance when it might be beneficial: (2) . A recent study conducted by Italian researchers found that children (3) immediately preceding and during blood tests experienced less pain than children whose mothers (4) during the procedure, or children whose mothers were present but (5) .
The research, led by Carlo Brown, MD, at the University of Siena, is published in the Archives of Disease in Childhood. (6) the study. None received any type of anesthesia; the children and their mothers (7) . Both the group whose mothers attempted to distract them from the blood tests and those whose mothers simply observed reported (8) than the group who watched cartoons. For that group, the levels of pain were less and the children were better able to (9) .
One of the possible explanations is that children might have (10) during the procedures, exacerbating their perception of pain. "The higher pain level reported by children during (11) shows the difficulty mothers have in interacting positively (12) in their children’s life," the authors write.
However, they stressed that (13) still provided benefits, noting that the children would (14) during the procedures. "Indeed, children state that having their parent present (15) when in pain," say the authors.
Another possibility offered for consideration is the notion that the (16) might release pain-quelling endorphins. Endorphins, (17) produced by the pituitary gland, resemble opiates in their ability to produce analgesia and a sense of well-being. In other words, they might (18) .
In any case, the study results suggest that health workers should (19) to watch television during painful procedures (20) .