how to solve this one problem

ssssss

In experiment in which certain kinds od bacteria were placed in a generous supply of nutrients, the population of bacteria grew rapidly, and genetic mutation occurred at random in the poplations. These experiments show that all genetic mutation is Random.

which one of the following , if ture, enable the conclusion to be properly drawn?

A either all genentic mutations are random or none are random.

B the bacteria tested in the experiments were of extremely common form

C if all genetic mutation in bacteria are random, then all genetic mutation in every other life form are random also

D the kind of enviroment in which genetic mutation takes place has no effect on the way genetic mutation occurs.

E the nutrients used were the same as those that nourish the bacteria in nature.

which one the right answear and why.

thx a bunch

   

roric

C

kingme

A

ssssss

why A?

jane1109

the answer is A, because it places 2 alternatives in front of the reader. And according to the passage, one of the alternatives would be rejected (none are random), thus the only one left is the only one acceptable (all are random).

mbaer

A

If you put A back into the stem, you can get the conclusion.

But C you can not. The given condition of C 'all genetic mutation in bacteria are random' is beyond the scope of the stem, which talks about 'genetic mutation occurred at random in the poplations',not 'all'.

fredshen

以下是引用ssssss在2006-8-7 16:31:00的发言：

How to solve this problem?

this is a justify conclusion question. A is abusrd, but it does make the argument air-tight.

Remember Justify and Assumption questions are different. Assumption questions are looking for assumption that is necessary for the conclusion to be reached. That it is has to be the missing piece in the argument. That is the speaker made a jump from evidence to conclusion.

Justify questions are different in a sense that the answer doesnt have to be  necessary for conclusion to be reached.  The answer is the piece to make the conclusion 100% valid follwing the logic.

In this question A is not an assumption made by the statement, but plug it into the argument will make the argument air-tight.  

[此贴子已经被作者于2006-8-9 1:57:09编辑过]

fredshen

以下是引用mbaer在2006-8-8 20:12:00的发言：

in bacteria are random' is beyond the scope of the stem, which talks about 'genetic mutation occurred at random in the poplations',not 'all'.

C is wrong on the count that it provides a useless condtion that does nothing to justfify the conclusion The job is to prove that conditon.