题目内容：
Ifyouhaveaheartdiseaseorcondition,high-intensityexerciseforlongstretchescouldactuallyincreaseyourchanceofamassiveheartattackorstroke,recentstudiesfound.
Inthefirstoftwostudies（1）inHeart,Germanresearchersspentadecadestudyingthe（2）andintensityofweeklyexercisein1,000peopleintheir60swithcoronaryarteryheartdisease(冠心病),almosthalfofwhomwere（3）2-4timesaweek.Predictably,participantswho（4）lessthan2timesaweekweredeterminedtobeatgreaterriskforaheartattack.However,counter-intuitively(直觉地),participantswhoexercisedmorethantheaveragewerealsotwiceaslikelytohaveaheartattackorstrokethantheaverage.
Adifferentstudyfoundthatyoungmenwhoengageinenduranceexercisemorethanfivehoursaweekmay（5）theirriskofdevelopinganirregularheartrhythmlaterinlife.
Swedishresearcherssurveyed44,000men,ages45-79,abouttheirexercise（6）atagesof15,30,50andoverin2013.Thosewhoexercised（7）formorethanfivehoursaweekwere19%morelikelytohavedevelopedanirregularheartbeat,whichisa（8）factorinstrokerisk.
Despitetheirfindings,researchers（9）soundingthealarmfull-forceonintenseexercise,citingthe"benefitsofexercise"whileclarifyingthat"thestudiesreviewedhere,andfuturestudies,willservetomaximizebenefitsobtainedby（10）exercisewhilepreventingundesirableeffectsofintenseexercise."
A．active
B．avoided
C．behavior
D．consequently
E．Density
F．Energetic
G．Engagement
H．Exercised
I．Frequency
J．Increase
K．Intensely
L．Key
M．Largely
N．Published
O．regular
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