Need answer asap
which best explains the difference between an element and a compound?
a. elements cannot occur naturally, while compounds naturally occur.
b. elements have specific properties, while compounds do not have specific properties
c. elements cannot be broken, while compounds can because they join together in a specific pattern
d. elements can be broken down, while compounds cannot because they are composed of two or more mixtures.

Last week i was assigned a thematic. we have groups of three but the people i was assigned with haven't been in school for days. i would appreciate if anyone can me with my thematic . i highlighted most of the important steps and i circled my thematic topic. in desperate need : ( its due on february 19

Identify the various levels of atmosphere. troposphere mesosphere exosphere stratosphere thermosphere

Which is an advantage of having memory cells when a pathogen is encountered for a second time. a) the memory cells are what proliferate into clones of cells in response to the binding of an antigen. b) memory cells are vital to the primary immune response in that they immediately recognize pathogens even at the first encounter. c) memory cells are essentially effector cells that are short lived and attack antigens even without having a receptor specific to that antigen. d) it ensures that more lymphocytes with a receptor specific to a particular antigen will be present than in a host that had never encountered that pathogen.