be, look, seem, sound
become

extremely, fairly, very, etc.
enormously, exceedingly, extraordinarily, highly, hugely, immensely, incredibly, infinitely
This is a highly complex matter.

especially, exceptionally, particularly
increasingly
relatively
surprisingly
unnecessarily
technically
technically complex surgery

Complex is used with these nouns:
area, arrangement, array, calculation, carbohydrate, chain, character, concept, construction, creature, design, detail, device, division, emergency, emotion, equation, explanation, flavour, form, formula, fraud, hierarchy, idea, instruction, interaction, issue, legislation, litigation, machinery, manoeuvre, matter, maze, mechanics, mechanism, melody, mix, mixture, molecule, narrative, nature, negotiation, network, number, organism, pattern, personality, phenomenon, picture, plot, problem, procedure, process, question, reality, relation, relationship, rhythm, sentence, sequence, series, set, shape, situation, society, story, structure, subject, sugar, system, tangle, task, technology, topic, undertaking, variation, version, web, whole, workings