it is not until rECEntly ______ thErE ArE mAny DiFFErEnt kinDs oF hEAring DEFECts.
A．hAvE thE sCiEntists DisCovErED
B．thE sCiEntists hAvE DisCovErED
C．thAt thE sCiEntists hAvE DisCovErED
D．thAt will thE sCiEntist hAvE DisCovErED