Questions

Humans cannot digest cellulose because they are lacking with the enzymes responsible to breakdown the beta acetal linkages.

The meanings of the given words are as follows:
Tremulous: shaking or quivering slightly 

Stringent: (of regulations, requirements, or conditions) strict, precise, and exacting

Garrulous: excessively talkative, especially on trivial matters
Quivery: shaking or trembling slightly
Steady: firmly fixed, supported, or balanced; not shaking or moving
Conjunctive: relating to or forming a connection or combination of things
Desist: stop doing something; cease or abstain

Abstain: restrain oneself from doing or enjoying something
Defer: put off (an action or event) to a later time; postpone
Terse: sparing in the use of words; abrupt
Abrupt: sudden and unexpected
Therefore, it can be observed that option B i.e. ‘quivery, steady’ forms a synonym-antonym pair of ‘tremulous’.

Options A, C and E in the absence of a proper subject add the ‘bag’ automatically to the verb ‘racing for the bus’. So, it does not make any sense as it would mean that the bag is racing for the bus. Option B is incorrect because of the fragment ‘making the documents lose’. Option D doesn't convey the proper meaning.

Troposphere is the most densest layer and is the lowest atmospheric layer.