strenuous

a.费力的

strawberry, strawberry-mark, stray, stray away from, streak, streaker, streaky, stream, stream of consciousness, streamline, streamlined, streamlining, street, street credibility (also ,street `cred), street value, street-girl (also `street-walker), street-wise, streetcar, strength, strengthen, strenuously, streptococcal, streptococcus, streptomycin, stress, stress mark, stressful, stretch, stretch out, stretcher, stretcher-bearer, stretchiness, stretchy, strew, strewth, striate, striated, striation, stricken, strict,