two LSAT questions. i need your help.

gracekelly

15. The only plants in the garden were tulips but they were tall tulips So the only plants in the garden were tall plants.
Which one of the following exhibits faulty reasoning most similar to the faulty reasoning in the argument above?
(A) The only dogs in the show were poodles and they were all black poodles. So all the dogs in the show were black.
(B) All the buildings on the block were tall. The only buildings on the block were office buildings and residential towers. So all the office buildings on the block were tall buildings
(C) All the primates in the zoo were gorillas. The only gorillas in the zoo were small gorillas. Thus the only primates in the zoo were small primates
(D) The only fruit in the kitchen was pears but the pears were not ripe. Thus none of the fruit in the kitchen was ripe
(E) All the grand pianos here are large. All the grand pianos here are heavy Thus everything large is heavy

I think the argument is right. However the key is C. why ?

18. Because dinosaurs were reptiles, scientists once assumed that, like all reptiles alive today, dinosaurs were cold-blooded. The recent discovery of dinosaur fossils in the northern arctic however has led a number of researchers to conclude that at least some dinosaurs might have been warm-blooded. These researchers point out that only warm-blooded animals could have withstood the frigid temperatures that are characteristic of arctic winters, whereas cold-blooded animals would have frozen to death in the extreme cold.
Which one of the following if true weakens the researchers' argument?
(A) Today's reptiles are generally confined to regions of temperate or even tropical climates
(B) The fossils show the arctic dinosaurs to have been substantially smaller than other known species of dinosaurs.
(C) The arctic dinosaur fossils were found alongside fossils of plants known for their ability to withstand extremely cold temperatures.
(D) The number of fossils found together indicates herds of dinosaurs so large that they would need to migrate to find a continual food supply
(E) Experts on prehistoric climatic conditions believe that winter temperatures in the prehistoric northern arctic were not significantly different from what they are today.
这道题我不知道想weaken 什么？如果是weaken 的结论，那么D 怎么weaken 的

mindfree

1. The argument is wrong. Tall tulip --> tall plant? So small elephant --> small animal?

2. D is right in that it suggests that the dinosaurs were not staying in arctic all the time. Read the question very carefully: frigid temperatures that are characteristic of arctic winters. So only winter is too cold for them. And they might migrate to other places in the winter.

Other choices are either irrelevant (A, B) or strenthen (C, E)