单选题：＿＿＿＿＿ it rain tomorrow, we would have to put off the visit t..

Only when 1 was fourteen__________the importance of study．A．I realizedB．did I realizeC．had I realizedD．I had realized

Only when your identity has been checked__________.A．you are allowed to come inB．You will be allowed to come inC．will you allow to come inD．will you be allowed to come in

A beam of light will not bend round corners unless______to do so with the help of a reflecting device .A．having been madeB．being madeC．madeD．you make

Never before in China _______ for the unemployed.A．has done so muchB．has been done so muchC．so much has been done　D．has so much been done

Only when possible to settle the problem.[ ]A. does the editor come will it beB. the editor comes will it beC. has the editor come it will be D. the editor comes it will be