CThereisnotenoughoilintheworldnow.Astimegoesby,itbecomeslessandless,sowhatarewegoingtodowhenitrunsout?Perhapswewillgobacktousinghorses,carriagesandbicycles.IntheSecondWorldWar,somepeopledidn’tuse

　　C

　　Thereisnotenoughoilintheworldnow.Astimegoesby,itbecomeslessandless,sowhatarewegoingtodowhenitrunsout?Perhapswewillgobacktousinghorses,carriagesandbicycles.

　　IntheSecondWorldWar,somepeopledidn’tusegasmadefrompetroleum(石油)intheircars.Theymadegasfromwoodandplantsinstead.Thecardidn’tgofast,buttheyran,sothiswasbetterthannothing.However,inthefuture,wecan’tcutdownallourtreestomakegas;weneedourtreesforotherthings,too.

　　Besidesdifferenttypesofgas,wecanalsouseelectricitytorunourcars,butfirstwemustmaketheelectricity!Somecountrieshavecoalandtheymakeelectricitywiththat,butwemightnotalwayshavecoal,either.Othercountrieshavebig,strongrivers,andtheycanusethepowerofwatertoturnturbines(涡轮机)andmakeelectricitymoreeasilyandcheaply.

　　Wearealsoabletogetpowerfromtheoceantides.Weputturbinesintothemouthoftheriver.Thenthetidecomesin,thewaterturnstheturbinesandthenitgoesout,itturnsthemagain.

　　Whichofthesewayswillbeusedtorunourcarsinthefuture?

　　49.Whenmightpeoplehavetogobacktousinghorsesandcarriages?

　　A.Whentheyarepoor. B.Whentheyrunoutofoil.

　　C.Whentheyneedmoreexercise. D.Whentherearen’tanybigtreesintheworld.

　　50.WhatdidsomepeopleusetomakegasintheSecondWorldWar?

　　A.Water B.Coal C.Woodandplants D.Tides

　　51.Howmanywaysaresuggestedtomakeelectricityinthepassage?

　　A.2 B.5 &nb