1. ostentatious : modest ::

A.

vigilant : lazy

B.

reticent : talkative

C.

visionary : blind

D.

ostensible : silent

E.

olfactory : loud

2. spectrum : range ::

A.

repartee : departure

B.

repertoire : music

C.

vigil : insomnia

D.

repose : bed

E.

surveillance : observation

1) Ostentatious : modest ⇒ B. Reticent : talkative

Ostentatious and modest are words whose definition are the exact opposite of one another. So, reticent and talkative fit the criteria of words that are antonyms.

2) Spectrum : range ⇒ E. Surveillance : observation

Spectrum is a condition that is not limited to a specific set of data or values.

Range is a condition that has limitations, from the smallest value to the largest value.

Surveillance and observation fits the criteria wherein observation can be done within a surveillance just as range is part of a spectrum.