LSAT 2004.12 section A

nidm

21. Although the geological record contains some hints of
major meteor impacts preceding mass extinctions, there
were many extinctions that did not follow any known
major meteor impacts. Likewise, there are many
records of major meteor impacts that do not seem to
have been followed by mass extinctions. Thus the
geological record suggests that there is no consistent
causal link between major meteor impacts and mass
extinctions.
Which one of the following assumptions enables the
argument’s conclusion to be properly inferred?
(A) If there were a consistent causal link between
major meteor impacts and mass extinctions,
then all major meteor impacts would be
followed by mass extinctions.
(B) Major meteor impacts and mass extinctions
cannot be consistently causally linked unless
many mass extinctions have followed major
meteor impacts.
(C) Of the mass extinctions that did not follow any
known major meteor impacts, few if any
followed major meteor impacts of which the
geological record contains no hints.
(D) If there is no consistent causal link between
major meteor impacts and mass extinctions,
then not all mass extinctions could have
followed major meteor impacts.
(E) There could be a consistent causal link between
major meteor impacts and mass extinctions
even if not every major meteor impact has
been followed by a mass extinction.

nidm

Answer is A, but I do feel B is much better. (A) seems too strong

ssssss

Premise 1: Although the geological record contains some hints of major meteor impacts preceding mass extinctions, there were many extinctions that did not follow any known major meteor impacts.

Premise 2: Likewise, there are many records of major meteor impacts that do not seem to have been followed by mass extinctions.

Conclusion: Thus the geological record suggests that there is no consistent causal link between major meteor impacts and mass extinctions.

Which one of the following assumptions enables the argument’s conclusion to be properly inferred?

This is an assumption question, bridging between premise and conclusion.

(A) If there were a consistent causal link between major meteor impacts and mass extinctions, then all major meteor impacts would be followed by mass extinctions.
This is the right answear and strengthen the argument. This directly support the argument’s conclusion.  

(B) Major meteor impacts and mass extinctions cannot be consistently causally linked unless many mass extinctions have followed major meteor impacts.
unless = if not

then we transfer it to:

If not many mass extinctions have followed major meteor impacts, meteor impacts and mass extinctions cannot be consistently causally linked.

Negate both side of conditional statement, we transfer it to:

If meteor impacts and mass extinctions can be consistently causally linked, many mass extinctions have followed major meteor impacts.

This is wrong because 因果
                倒置  .

(C) Of the mass extinctions that did not follow any known major meteor impacts, few if any followed major meteor impacts of which the geological record contains no hints.

This is out of the sphere.

(D) If there is no consistent causal link between major meteor impacts and mass extinctions, then not all mass extinctions could have followed major meteor impacts.

(E) There could be a consistent causal link between major meteor impacts and mass extinctions even if not every major meteor impact has been followed by a mass extinction.

This is weakening the conclusion.