The earliest stage in the chart appears very similar for all three species. For example, all three embryos at this stage have gill slits and a large embryonic tail. What do these similarities most likely indicate?

a "theory" a suggestion that is not 100 % accurate, or a figure. some people say its a theory because they of all the passed theory's about one subject. it depends sometimes theory might be accurate and sometimes they are.

the three components of a nucleotide are the nitrogenous base, the phosphate group and the five-carbon sugar.

measuring light intensity

light meters can be used to measure light intensity. the meter is held at the soil surface and pointed in the direction of the maximum light intensity, and then the meter is read.

errors can be made when measuring light intensity by accidentally shading the light meter. the reliability of the results can be checked by taking many samples.