Teenagers are different from people of other age grou

ps. The differences can be 18) from how they behave. In fact, the brains of teenagers are very different from those of children or adults.

Once people believed it was 19) that the human brain was fully developed by the age of three. According to this theory, teenager behaviors like risk-taking, a lack of sensitivity to how their actions 20)both themselves and others, increased aggressive deeds, 21) concentration and a negative attitude were thought to be due to bad parenting or changes in body chemistry.

However, new technology has allowed researchers to examine the healthy brain at work. What they have discovered is something 22) : Not only does the brain continue to grow beyond the age of three, but the research also23) that the brain of a teenager is larger than that of an adult.

As teen brains are 24) with chemicals during adolescence phase, the brain grows. However, only the cells that are used the most will 25) the competition within the brain. Those that are used less begin to die off until the brain reaches what will be its adult size.

The way that teens spend their time 26) influences which connections remain and which disappear. On the basis of this knowledge, experts advise parents to be 27) on how their teenagers spend their time. What teens do today will affect their brains for the rest of their lives.

A) diminished

B) demonstrated

C) alert

D) radical

E) surrender

F) survive

G) affirms

H) afford

I) affect

J) effect

K) soaked

L) soaped

M) sensitive

N) sensible

O) somehow