Although the scientist claimed to have made a major breakthrough in his research, the evidence he offered as proof of his assertion was at best.
(a) conclusive
(b) indubitable
(c) paltry
(d) copious
(e) extensive

modal adverbs are used to modify specific verbs that consist of a linking verb (verb of being) and sometimes another verb. examples of modal verbs include can, could, may, might, must, shall, should, will and would.

modal auxiliary. an auxiliary verb characteristically used with other verbs to express mood, aspect, or tense. in english, the most common modal auxiliaries are can, could, may, might, must, ought, shall, should, will, and would. also called modal .