B. Too much the rein: the strongest oaths are straw
Iambic pentameter has 5 metric feet called iambs. The iambs are made of an unstressed syllable followed by a stressed syllable. This means that a line of iambic pentameter has 10 syllables. Option A: Though/ eve/ry /drop/ of/ wa/ter /swear/ ag/ainst/ it/ has 11 syllables. Option B: Too/ much/ the/ rein/: the/ stron/gest/ oaths/ are/ straw/ has 10 syllables. Option C: Good/ wombs/ have/ borne/ bad/ sons/ has 6 syllables. Option D: And/ left/ me/ to/ a/ boot/less/ in/qui/si/tion/ has 11 syllables. The only choice with 10 syllables is B. If you were to write out the unstressed syllables it would look like this: too MUCH the REIN: the STRONgest OATHS are STRAW.