_________(57)A.pressure B.restraintC.load D.weight

According to the fifth rule, a pressure cooker cover should be opened______ .A．as soon as

A pressure drop in the liquid line of a refrigeration system may cause________.A.the solen

57._________A. recipesB. projectsC. receiptsD. in

57._________A.smallB.hugeC.simpleD.colorful

57._________A. chooseB. watchC. drawD. recognize

57._________A. whereB. whatC. thatD. how