[" 20.The compounds "A" and "B" in the following "],[" reaction are respectively "],[qquad quad Aquad (HCHO+HCl)/(O)AAgCN=B],[" (b) "A=" benzyl chloride,"B=" benzyl isocyanide "],[" (b) "A=" benzyl alcohol,"B=" benzyl isocyanide "],[" (c) "A=" benzyl alcohol,"B=" benzyl cyanide "],[" (d) "A=" benzyl chloride,"B=" benzyl cyanide "]