The levels of carbon dioxide in the atmosphere a. began decreasing when the burning of fossil fuels increased. b. are estimated to be higher than at any time in the past 420,000 years. c. are high but not higher than the highest estimated levels in the last 420,000 years. d. peaked around 1950 and have begun slowly decreasing since then.

The levels of carbon dioxide in the atmosphere are estimated to be higher than at any time in the past 420,000 years. That is option B

CARBON DIOXIDE is a very harmful compound which is easily released into the atmosphere through burning of fossil fuels and other carbon compounds in plenty of air. This is a green house as which is capable of building up in the atmosphere and contributing to the green house effect. The unabsorbed carbondioxide rises to the upper atmosphere and blocks the radiation of solar energy back into the space. This precipitates a global temperature increase called the greenhouse effect.

According to Intergovernmental Panel on Climate Change (IPCC) in a current research discovered that CO2 concentration in the earth’s atmosphere is higher than at any point during the last 650,000 years. They where able to study this through the study of higher levels of CO2 concentration which coincide with higher temperatures.

Therefore the correct option is B which states that the levels of CARBON DIOXIDE in the atmosphere are estimated to be higher than at any time in the past 420,000 years.

You can learn more about carbondioxide as a pollutant here:

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.

6.4 cm (max) - 25 cm (min)