4. What do scientists think they will learn to do with embryonic stem cells

A. Save extinct or endangered species.

B. Clone family pets.

C. Allow people to genetically engineer the characteristics of their children.

D. Improve a person's immune system and repair damaged tissue.

Of the pollutants that form acids in the atmosphere, which is easiest to reduce? a. sulfur dioxide b. nitrogen dioxide c. ozone d. carbon monoxide

The table shows dates and appearance of index fossils. which rock layers can be dated most precisely? a) a layer containing both a fossil 4 and a fossil 3 b) a layer containing both a fossil 2 and a fossil 3 c) a layer containing both a fossil 1 and a fossil 4 d) a layer containing both a fossil 1 and a fossil 2

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.