每日一题

141. One way to do this is to find a sheltered roost. Solitary roosters shelter in dense  vegetation or enter a cavity-horned larks dig holes in the ground and ptarmigan burrow into  snow banks-but the effect of sheltering is magnified by several birds huddling together in  the roosts, as wrens, swifts, brown creepers, bluebirds, and anis do.  The word "magnified" is closest in meaning to which of following?