What are wavy features found on some sandstones?

Long term exposure to waves can cause sunburns and skin cancer.

Dna. we have heard that we are a product of our dna. but where is it? how do we "get" our dna? it is passed to us, from our parents, but in what form? several vocabulary words associated with inheritance are used interchangeably and sometimes, incorrectly. let's see if you can clear this up for someone just learning about inheritance and cell structure.

Gram-negative bacteria have a cell wall that is! and does not accept the stain, making itappear