Which Experimental Observation Led Scientists to Speculate That Cathode Rays

Multiple Choice

Which experimental observation led scientists to speculate that cathode rays contained particles that were constituents of all matter?

A) The rays were deflected by electrical fields.
B) The rays were deflected by magnetic fields.
C) The rays were independent of the type of gas in the vacuum tube.
D) All of the above provided evidence of the "fundamental" nature of cathode rays.