{{B}}quEstions 16 to 20 ArE BAsED on thE Following tAlk.{{/B}}

A、no onE But thE sCiEntists know whAtEsp rEAlly is.
B、EvEryBoDy hAs thE ExpEriEnCE oFEsp.
C、it is impossiBlE to DECiDE whEthEr onE hAsEsp or not.
D、Esp hAs BEEn stuDiED By mAny pEoplE.