TRUMP's WRONG TOO: "Trump: "A Pyramid Is A Solid Structure," "You Don't Put Grain In A Pyramid, It Is All Solid" | Video | RealClearPolitics

They are not completely solid. They do have chambers. And in Carson's defense, I think he just said,in an off-hand manner, that it is plausible that they were used for grain. I don't think he was saying it as an absolute,nor that he was trying to persuade people such was the case.

http://www.realclearpolitics.com/video/2015/11/09/trump_a_pyramid_is_a_solid_structure_you_dont_put_grain_in_a_pyramid_it_is_all_solid.html