Gypsum has a hardness of 2 and quartz has a hardness of 7. explain why gypsum can not scratch quartz.

Which technically is nasa developing that will astronauts reach mars

If a robot fixed another robot is it a engineer or doctor?

1. fold your hands together so your thumbs cross over ,and look at your thumbs. which thumb feels most "comfortable" on top is actually controlled by a gene. the left thumb folding over the right thumb is a domi