compulsory

a.必须的；义务的

compound sentence, compound-interest, comprehend, comprehensibility, comprehensible, comprehension, comprehensive, comprehensive insurance, comprehensive school, comprehensively, comprehensiveness, compress, compression, compressor, comprise, compromise, compulsion, compulsive, compulsively, compulsorily, compunction, computation, computational, compute, computer, computerization, computerization, -isation, computerize, computerize, -ise, computing, comrade, comrade-in-arms n (pl comrades-in-arms), comradely, comradeship, con, con man, concatenate, concatenation, concave, concavity,