What is the rhyme scheme of a shakespearean sonnet?
a. abab cdcd efef gg
b. abab bcbc cdcd ee
c. abba abba cdc cdc
d. abba bcdc ded ded

The rhyme scheme of a Shakespearean sonnet is A. abab cdcd efef gg

Here is an example of a Shakespearean sonnet. 
It is SONNET II by William Shakespeare

When forty winters shall besiege thy brow, - A
And dig deep trenches in thy beauty's field, - B
Thy youth's proud livery so gazed on now, - A
Will be a totter'd weed of small worth held:  - B
Then being asked, where all thy beauty lies, - C
Where all the treasure of thy lusty days; - D
To say, within thine own deep sunken eyes, - C
Were an all-eating shame, and thriftless praise. - D
How much more praise deserv'd thy beauty's use,- E
If thou couldst answer 'This fair child of mine - F
Shall sum my count, and make my old excuse,' - E
Proving his beauty by succession thine! - F
   This were to be new made when thou art old, - G
   And see thy blood warm when thou feel'st it cold. - G