回答下列各题 We do not know how the first fire was 21 ．Early fires on the earth were ce

rtainly caused by nature，not by Man，some were caused by lightning in a storm；22 ，perhaps，by the hot material which came out of a volcano．Quite possibly，at times，the heat of the sun set light 23 some dry grass or leaves．At first Man，like other animals，was probably afraid of fire． 24 great was the power of fire that he feared it and worshipped it．Gradually，however，with his better power of thinking，he overcame his fear．Probablly he overcame most of his fear when he 25 how to make fire for himself．Throughout the ages he has learned more about fire，how to control it，and how to use it 26 many ways．Now fire is no longer a master of a god；it is a 27 ． We call only guess how 28 first learned that a fire was useful and what uses he made of it．By 29 a burning stick from fire which had been started naturally，he could make afire at his own“home”．He could keep the fire burning by adding more dry grass．1eaves and wood．The‰30 the chief purpose of frightening animals away．He discovered，by some accident，that flesh roasted in front of a fire 31 better．Then he found that roasted flesh would keep longer，without going bad， 32 uncooked flesh．It must have been much later that Man learned to cook food by heating it with 33 water or with steam．He could not use such methods 34 he had learned how to make pots 35 holding water．

A.made

B.produced

C.given

D.opened