An online dictionary and an online thesaurus
a. are often linked together.
b. will most often suggest words for you to define.
c. are best used only when paper editions are not available.
d. often contradict one another unless the search field is used.

#1  sara was always tasked with selecting birthday presents for her friends and family because everyone admired her  impeccable taste. 

impeccable (adj): perfect, flawless

#2  they moved to the united states many years ago, but their  insular  attitudes made it difficult for them to socialize. 

insular (adj): isolated; separate

#3  the professor explained the  semantic  relationship between the two nouns used in the sentence. 

semantic (adj): related to words or the meanings of words 

happy to : )

i am also pretty sure it is c

assuming the underlined word is "regnant", the correct answer is b) ruling.