Spread Sector someone, option, points, credit

jbaldyga

in the mock 2010 exam.

it states

spreads to narrow in all other spread sectors,
a positively sloped yield curve with short rates rising 25 basis points and long rates rising by about 75 basis points

option

A. lengthen duration in all spread sectors.
B. lengthen duration in the credit sector and shorten it in the Treasury sector.

a seems like it could be an answer too, can someone explain