A:乙酸与碳酸氢钠溶液反应:2CH3COOH+CO32 ='=' 2CH3COO-+CO2↑+H2O
B:醋酸溶液与新制氢氧化铜反应:2H十+Cu(OH)2 ==Cu2++2H2O
C:苯酚钠溶液中通入少量二氧化碳:2C6H5O-+CO2+H2O →2C6H5OH+CO32-
D:甲醛溶液与足量的银氨溶液共热:
He has ________ in touch with his foreign friends for many years.