Which statement describes the best example of an observational study? O A. A scientist measures the height of different mountains in Asia.
O B. A scientist measures the height of trees before and after they are
given fertilizers.
O C. A scientist measures the speed of a river without a dam and
compares it to the speed of a river with a dam.
O D. A scientist measures the weight of bears in protected habitats and
compares it to the weight of bears outside protected habitats.

I am really sorryeiyy e mail address through I

Explanation:

judge I expect you to get the latest flash and I will

I am really sorry I am really sorry I missed the first

answer: - b cells

explanation: -

so, the b cells mediate their action by identifying the antigens present on the surface of the pathogens and then producing antibodies in return to mediate its effect.

the answer is: the „power stroke“ step.

muscle contraction can be divided into a few steps:

1. the release of ach (acetylcholine) in the synaptic cleft, binding of ach for its receptor and consequently opening of the ca channels.

2. the release of ca, binding of ca for the troponin

3. troponin shifting the tropomyosin, which was blocking the active site on the actin

4. myosin heads attaching to actin by breaking down atp to adp+ pi

5.   formation of the ‘cross-bridge’ on the active site of the actin filament by myosin head

6. “power stroke” -the cross bridge pulls actin, which slides over the myosin

9.     7. the release of adp completes the cross-bridge movement and atp attaches to myosin, breaking the actin-myosin cross bridge.