Recognizing duplicate pairs of words

The exact matches are in boldface; the unmatched words are noted, with their difference:

1. quadrilateral AND quadriateral

\["l" is missing from the second word\]

1. obtuse AND obtuse

\[exact match\]

1. isosceles AND isoseles

\["c" is missing from the second word\]

1. circumference AND circumference

\[exact match\]

1. radian AND radian

\[exact match\]

The correct response is three.