[B]

Vitamins, like minerals, are chemicals. There is
absolutely not difference in the chemical structure
(11)
of the nature vitamin C and the chemical structure
(12)
of the synthetic vitamin C. Also, while most sub-
stance are harmless at very low level of intake, all
(13)
substances —— even elements that are essential to life ——
can be dangerous if you overdo them. Take water
for example. Six or eight glasses a day will keep your
body in good fluid balance. But you can also be drown
(14)
in it. Some people argue that individuals vary greatly
(15)
in their need for nutrients, it cannot necessarily    be
stated any given amount is too much; that is all
(16)
relative. But since there is little solid information
on what is the optimal intake of any essential nutrient in
healthy individuals, it would be impossible to give
guidelines that take these proportional needs into the
(17)
account. Just as with other drugs, the relation to
(18)
different vitamin dosages varies, with some people
better able than others to tolerate large amounts. While
we do know that very specifically what the toxic level
(19)
is for vitamin A and D, we are far less sure about
vitamin E, even though it, too, is fat-soluble, and we
still don't understand the water-soluble vitamin, the C
(20)
and the B groups, which the body can't store.

[C]

The telephone system is a circuit-switched network.
For much of the history of the system, when you placed
(21)
a call, you were renting a pair of copper wires that ran
continuously from your telephone to the other party's
phone. You had excluding use of those wires during the
(22)
call; when you hung up, they were rented to someone
else. Today the translation is more complicated. (your call
may well possess a fiber-optic cable or a satellite with
hundreds of other calls), but more conceptually the system
(23)
still works the same way. When you dial the phone, you get
a private connection to one other party.

This is an alternative network architecture called
(24)
packet switching, in which all stations are always connected
to the network, but they receive only the message addressed
to them. It is as if your telephone was always turned in to
(25)
thousands of conversations going on the wire, but you
(26)
heard only the occasional word intended to you. Most
(27)
computer networks employ packet switching, because
it is more efficient than circuit switching when traffic
is heavy. It seems reasonable the existing packet-switched
(28)
network will grow, and new one may be created; they could
(29)
well absorb traffic that would otherwise go to the telephone
system and thereby reduce the need for telephone numbers.
(30)