With the help of high technology, more and more new substances ___in the past few years.

A．discovered

B．have discovered

C．had been discovered

D．have been discovered

患者，女，71岁，全牙列缺失，曾行全口义齿修复，自诉上颌义齿固位较差，下颌尚可。口腔检查发现上、下颌弓关系正常，上颌牙槽嵴吸收较重。重新进行全口义齿修复。

进行平衡调整时，前伸平衡的情况下，后开至少有（）。

A.两点接触

B.三点接触

C.四点接触

D.多点接触

E.完全接触