"Grace" rhymes with "ways": choice B. This may seem a little odd, as the two words don't exactly rhyme. This kind of imperfect rhyme is called a slant rhyme. Slant rhymes often rely on assonance (i.e., vowels that sound alike) to create the sense of rhyme. Significantly, both "ways" and "grace" are dominated by a long "a" sound, an assonance that ties the words together. Further, while the "c" in grace is softer than the "z" sound of ways, those two sounds are similar.

We know these are the words that are meant to rhyme because this is a Petrarchan sonnet. A Petrarchan, or Italian sonnet, is broken into two parts: a first part of eight lines and a second part of six lines. Barrett Browning has divided her first eight lines into two quatrains that rhyme according to the following pattern: ABBA. The word at the end of the first line, "ways," is meant to rhyme with the word at the end of the fourth line, "grace."

In "Sonnet 43," Elizabeth Barrett Browning uses rhyme to convey passion and feeling. Browning’s use of rhyme creates a lyrical rhythm which flows perfectly as she addresses the depth of her passion for her beloved. 

The correct answer to your question is 'B.' In the opening line of the poem, Browning poses one of the most well-known questions in poetry--"How do I love thee? Let me count the ways."  Remember, rhyme is the repetition of familiar sound in words.  ‘Grace’ rhymes with ‘ways,’ because of the repeating vowel sounds (a).   Browning’s poem continues to rhyme throughout, consistent to the traditional rhyme scheme for most sonnets which is ABBA ABBA CD CD CD.