low level echo低密度: low-density回声: echo; bounce back; reverbera ...稀: rare; scarce; uncommon硫: sulphur; sulfur回波: echo; return waves下载手机词典可随时随地查词查翻译关注微信公众号：chachacidian，回复:低密度回声,稀硫回波,稀疏回波，即可在微信中查询翻译
