{{B}}pAssAgE 28{{/B}}

in EvEry DAy usAgE "hot" mEAns "hAving A lot oF hEAt". mAny pEoplE think thAt "ColD" is somEthing ComplEtEly sEpArAtED From hEAt.But this is not truE. "ColD" simply mEAns "hAving vEry littlE hEAt." your liFE DEpEnDs on hEAt. in FACt, EvEry living thing DEpEnDs on it. (28) {{u}}without hEAt, EvEry living thing woulD BE FrozEn to DEAth.{{/u}}All living things gEt thEir hEAt From thE sun, whiCh proviDEs thE ConDitions in whiCh liFE is possiBlE. sinCE thE DAwn oF history, mAn hAs BEEn ABlE to mAkE his own hEAt. hE hAs BEEn ABlE to rElEAsE thE sun’s hEAt thAt is trAppED in things suCh As wooD, CoAl AnD oil.AnD hE hAs BEEn ABlE to usE this hEAt. hEAt hAs mADE CivilizAtion possiBlE. with hEAt, mAn CoulD mElt mEtAls.As mAn lEArnED to usE mEtAls AnD FuEls, inDustriEs grEw.As A rEsult, EnginEs wErE invEntED、thEsE ArE mAChinEs thAt ChAngE hEAt EnErgy into mEChAniCAl EnErgy.EnginE CAn Do thE work oF mAny mEn. without EnginEs inDustriAl CivilizAtion is impossiBlE. yEt whEn thE First EnginEs wErE Built in thE 17th CEntury, mEn wErE still wonDEring ABout thE nAturE oF hEAt. "whAt is it " thEy AskED、not until thE EArly yEArs oF 19th CEntury DiD thEy FinD thE right AnswEr.

From thE lAst two sEntEnCEs, wE CAn sEE______.A．mEn hAvE nEvEr FounD thE nAturE oF hEAt
B．mEn FounD thE nAturE oF hEAt in thE 17th CEntury
C．mEn FounD thE nAturE oF hEAt in thE 19th CEntury
D．mEn FounD thE nAturE oF hEAt BEForE thE 19th CEntury