One of the questions of interest in the study of the evolution of spid

One of the questions of interest in the study of the evolution of spiders is whether the weaving of orb webs evolved only once or several times. About half the 35,000 known kinds of spiders make webs; a third of the web weavers make orb webs. Since most orb weavers belong either to the Araneidae or the Uloboridae families, the origin of the orb web can be determined only by ascertaining whether the families are related.Recent taxonomic analysis of individuals from both families indicates that the families evolved from different ancestors, thereby contradicting Wiehle’s theory. This theory postulates that the families must be related, based on the assumption that complex behavior, such as web building, could evolve only once. According to Kullman, web structure is the only characteristic that suggests a relationship between families. The families differ in appearance, structure of body hair, and arrangement of eyes. Only Uloborids lack venom glands. Further identification and study of characteristic features will undoubtedly answer the question of the evolution of the orb web.

17. The primary purpose of the passage is to
(A) settle the question of whether orb webs evolved once or more than once
(B) describe scientific speculation concerning an issue related to the evolution of orb
webs Spot on. This is the only one that makes sense. It just describes the issue.
A) it was never settled. C narrows the scope too far. It's looking at more spiders than those two. D it doesn't question any of their methods. E it doesn't really claim this. It just says one of the scientists claims this.

(C) analyze the differences between the characteristic features of spiders in the
Araneidae and Uloboridae families
(D) question the methods used by earlier investigators of the habits of spiders
(E) demonstrate that Araneidae spiders are not related to Uloboridae spiders

18. It can be inferred from the passage that all orb-weaving spiders belong to types of spiders that

(A) lack venom glands
(B) are included either in the Uloboridae or Araneidae families
(C) share few characteristic features with other spider types
(D) comprise less than a third of all known types of spiders
orb weaving spiders are 1/3 or about 1/2 of all spiders. that's 1/6 which < 1/3. Bingo
(E) are more recently evolved than other types of spiders

19. According to the passage, members of the Araneidae family can be distinguished
from members of the Uloboridae family by all of the following EXCEPT:
(A) the presence of venom glands
(B) the type of web they spin
This was the toughest one for me but I just checked it off in the passage. it doesn't say that you can distinguish the 2 by their web type. if anything it probably means they're the same
(C) the structure of their body hair
(D) the arrangement of their eyes
(E) their appearance

20. Which of the following statements, if true, most weakens Wiehle’s theory that
complex behavior could evolve only once?
(A) Horses, introduced to the New World by the Spaniards, thrived under diverse
climatic conditions.
(B) Plants of the Palmaceae family, descendants of a common ancestor, evolved
unique seed forms even though the plants occupy similar habitats throughout the
world.
(C) All mammals are descended from a small, rodentlike animal whose physical
characteristics in some form are found in all its descendants.
(D) Plants in the Cactaceae and Euphorbiaceae families, although they often look
alike and have developed similar mechanisms to meet the rigors of the desert,
evolved independently. I don't believe in evolution but just observing the reasoning here only D makes sense. We need an example of behavior (even plant behavior) where two unrelated things do the same thing. Of these choices only D provides this.
(E) The Cuban anole, which was recently introduced in the Florida wilds, is quickly
replacing the native Florida chameleon because the anole has no competitors