Lemon juice has a ph of about 2.0, compared to a ph of about 1.0 for stomach acid. therefore, the concentration of h+ in stomach acid is than that of lemon juice.

The concentration of h+ in stomach acid is  times more than that of lemon juice.

Explanation:

Basically, pH is a value that rates how acidic or alkaline a solution is on a scale from 0–14. A pH of 7 is considered neutral. Any pH value below 7 is considered acidic and any pH value over 7 is considered alkaline. Acidic solutions have a lower pH, while basic solutions have a higher pH.

On the pH scale, the difference between adjacent numbers represents a tenfold difference in acidity. For instance, a pH of 4 is 10 times more acidic than a pH of 5 and 100 times more acidic than a pH of 6.

Since the lemon juice has a pH of about 2.0 compared to stomach acid with a pH of about 1.0 It means that the the stomach acid is 10 times more acidic than the lemon juice.

pH = -log10[H+]

[H+] = 10^-pH

In Lemon juice;

[H+] = 10^-pH = 10^-2 = 0.01

In stomach acid;

[H+] = 10^-pH = 10^-1 = 0.1

0.1 is 10 times more than 0.01.

1. the question asks the most appropriate, which seems to rule out "all of the above." your choice appears to be the correct one.

2. the protocol described is good for identifying correlation, but not cause and effect. for cause/effect, you need to devise a protocol that will assign the treatment (or not) to groups that have essentially the same "demographics" with respect to all the other variables. your choice regarding control group seems appropriate. random assignment of treatment (choice d) may be appropriate also. (i think you can argue that b and d are just different descriptions of the same method.)

3. d will randomize the birds, but may not guarantee there are 10 in each group. e will do both, so seems the better choice.

comment on question 2

based on the problem statement, it seems clear that confident, attentive drivers are more likely to use daytime running lights. so, the protocol might need to be devised in such a way that the lights would be turned on or off without the driver's knowledge. (an attentive driver will figure it out.) assigning a confident, attentive driver to a group required to drive without running lights might mess with his/her confidence and attentiveness. you don't want your experiment to do that. (nor do you want the experiment to subject a driver to greater risk of accident as a consequence of driving without running lights.) experiments involving human safety are always problematic.