Must be studying

studying - perusing, perusal, hit the books, review, work, cram, read, learn, be taught, explore, research, analyze, look into, examine, conduct a survey of, investigate, appraise, inquire into, observe, watch, look at, eye, eyeball, scrutinize, regard

must - essential, a necessity, a requisite, a requirement, not to be missed, very good, mold, moldiness, mustiness, mildew, decay, fustiness, rot, be obliged to, have (got) to, need to, be compelled to, be required to, should, ought to

be - breathe, live, be extant, draw breath, exist, have life, be alive, have existence, have being, happen, take place, arise, transpire, materialize, occur, fall, crop up, come to pass, ensue, come about, befall, betide, be set, be positioned, be present