GWD4-20 & 5-4

Refer to "Which of the following is an assumption on which the
argument depends?" from two questions below, I  can not understand  and  confused about  what it asked?   Please help me  figure  out  these questions.  Thanks.
                

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Q40.

Many people suffer an allergic reaction to certain
sulfites, including those that are commonly added to wine as
preservatives.  However, since there are
several wine makers who add sulfites to none of the wines they produce, people
who would like to drink wine but are allergic to sulfites can drink wines
produced by these wine makers without risking an allergic reaction to sulfites. 

Which of the following is an assumption on which the
argument depends?

A.   
These wine makers
have been able to duplicate the preservative effect produced by adding sulfites
by means that do not involve adding any potentially allergenic substances to
their wine.

B.   
Not all forms of
sulfite are equally likely to produce the allergic reactions.

C.   
Wine is the only
beverage to which sulfites are commonly added.

D.   
Apart from
sulfites, there are no substances commonly present in wine that give rise to an
allergic reaction.

E.    
Sulfites are not
naturally present in the wines produced by these wine makers in amounts large
enough to produce an allergic reaction in someone who drinks these wines.            

Ans:E

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Q4:

In the past the country of Siduria has relied heavily on
imported oil.  Siduria recently
implemented a program to convert heating systems from oil to natural gas.  Siduria already produces more natural gas
each year than it burns, and oil production in Sidurian oil fields is
increasing at a steady pace.  If these
trends in fuel production and usage continue, therefore, Sidurian reliance on
foreign sources for fuel should decline soon.

Which of the following is an assumption on which the
argument depends?

1. In
        Siduria the rate of fuel consumption is rising no more quickly than the
        rate of fuel production.
2. Domestic
        production of natural gas is rising faster than is domestic production of
        oil in Siduria.
3. No
        fuel other than natural gas is expected to be used as a replacement for
        oil in Siduria.
4. Buildings
        cannot be heated by solar energy rather than by oil or natural gas.
5. All
        new homes that are being built will have natural-gas-burning heating
        systems.