题目内容：
根据以下材料，回答题
SharksPerformaServiceforEarth'sWaters
Itishardtogetpeopletothinkofsharksasanythingbutadeadlyenemy.Theyarethoughtto（1）peoplefrequently.Butthesefishperforma（2）serviceforearth'swatersandforhumanbeings.Yetbusinessandsportfishingarethreateningtheir（3）.Somesharksareatriskofdisappearingfrom（4）
Warmweathermayinfluencebothfishandsharkactivity.Manyfishswimnearcoastalareas（5）theirwarmwaters.Expertssaysharksmayfollowthefishintothesameareas,（6）peoplealsoswim.Infact,mostsharksdonotpurposelychargeatorbitehumans.Theyarethoughttomistakeaperson（7）aseaanimal,suchasasealorsealion.Thatiswhypeopleshouldnotswimintheoceanwhenthesungoesdownorcomesup.Thosearethe（8）whensharksarelookingforfood.Expertsalsosaythatbrightcolorsandshinyjewelrymaycausesharkstoattack.
Asharkhasanextremelygoodsenseofsmell.Itcanfindsmallamountsofsubstancesinwater,suchasblood,bodyliquidsand（9）producedbyanimals.Thesepowerful（10）help
sharksfindtheirfood.Sharkseatfish,any（11）sharks,andplantsthatliveintheocean.
Medicalresearcherswanttolearnmoreabouttheshark'sbodydefense,andimmune（12）againstdisease.Researchersknowthatsharks（13）quicklyfrominjuries.Theystudythesharkinhopesoffindingawaytofighthumandisease.
Sharksareimportantfortheworld's（14）.Theyeatinjuredanddiseasedfish.Theirhuntingactivitiesmeanthatthenumbersofotherfishinoceanwatersdonotbecometoo（15）.Thisprotectstheplantsandotherformsoflifethatexistintheoceans.
回答(1)题 A．Attack
B．meet
C．love
D．visit
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