Directions: In each of the following questions, select the related number from the given alternatives.

3:81 :: 6:?

Select the option in which the pair of letter-clusters share the same relationship as that shared by the given pair of letter-clusters.
CRO : FUR :: ? 

Select the option that is related to the fourth term in the same way as the first term is related to the second term and the fifth term is related to the sixth term.
 18 : 234 :: ? : 176 :: 14 : 126

Select the option that is related to the third number in the same way as the second number is related to the first number and the sixth number is related to the fifth number.
 37 : 100 :: 24 : ? :: 29 : 76

Select the option that is related to the third word in the same way as the second word is related to the first word. (The words must be considered as meaningful English words and must not be related to each other based on the number of letters/number of consonants/vowels in the word)
 Plants : Botanist :: Animals : ?

Select the option that is related to the third term in the same way as the second term is related to the first term and the sixth term is related to the fifth term.
 21 : 196 :: 29 : ? :: 38 : 315

Select the option that is related to the third word in the same way as the second word is related to the first word. (The words must be considered as meaningful English words and must not be related to each other based on the number of letters/number of consonants/vowels in the word.)
 Rice : Grain:: Lentils: ?

Select the option that is related to the third number in the same way as the second number is related to the first number and the sixth number is related to the fifth number.
 687 : 612 :: 713 : ? :: 621 : 546