一杯いかがですか。

amount necessary to fill a container (e.g. cupful, spoonful, etc.); drink (usu. alcoholic); full; one squid, octopus, crab, etc.; one boat; fully; to capacity; a lot; much; all of ...; the entire ...

how; in what way; how about

be; is

indicates a question (sometimes rhetorical); or; whether or not; some- (e.g. something, someone); indicates doubt, uncertainty, etc.; emphatic prefix; suffix forming adjectives or adverbs; in that way