Question at position 2 Which of the following statements about the carbon cycle are trueI. The major cause of increased atmospheric CO2 levels is increased photosynthetic activity resulting from modern agriculture.II. Like the nitrogen cycle, the carbon cycle has a gaseous form. III. Atmospheric CO2 levels have increased in modern history largely due to fossil fuel burning.IV. Rising atmospheric CO2 levels are a direct result of ozone depletion.II., III and IV.II. and III.I., II., III. and IVI. and III.Clear my selection单项选择题
A
II., III and IV.
B
II. and III.
C
I., II., III. and IV
D
I. and III.

Question

Question at position 2 Which of the following statements about the carbon cycle are trueI. The major cause of increased atmospheric CO2 levels is increased photosynthetic activity resulting from modern agriculture.II. Like the nitrogen cycle, the carbon cycle has a gaseous form. III. Atmospheric CO2 levels have increased in modern history largely due to fossil fuel burning.IV. Rising atmospheric CO2 levels are a direct result of ozone depletion.II., III and IV.II. and III.I., II., III. and IVI. and III.Clear my selection单项选择题

A

II., III and IV.

B

II. and III.

C

I., II., III. and IV

D

I. and III.

BlackTom AI · Accepted Answer

To tackle this question about the carbon cycle, I’ll evaluate each statement on its own before tying them together with the options.
Option 1: I. The major cause of increased atmospheric CO2 levels is increased photosynthetic activity resulting from modern agriculture. This is incorrect. The dominant driver of the modern rise in atmospheric CO2 is the burning of fossil fuels (coal, oil, and natural gas) and, to a lesser extent, deforestation. Photosynthesis generally removes CO2 from the atmosphere, not increases it, so attributing rising CO2 to increased photosynthetic activity is a mischaracterization of the carbon cycle.
Option 2: II. Like the nitrogen cycle, the carbon cycle has a gaseous form. This statement is true. The carbon cycle includes gaseous CO2 in the atmosphere as a key reservoir, just as nitrogen has gaseous forms (e.g., N2) in the atmosphere. Carbon also moves between air, oceans, vegetation, and soils, with CO2 gas playing a central role.
Option 3: III. Atmospheric CO2 levels have increased in modern history largely due to fossil fuel burning. This statement is true. The rapid rise in atmospheric CO2 over the past century is strongly linked to combustion of fossil fuels for energy and transportation, which releases significant amounts of CO2.
Option 4: IV. Rising atmospheric CO2 levels are a direct result of ozone depletion. This claim is incorrect. Ozone depletion affects UV radiation levels and has indirect climate effects, but it is not the direct cause of the rise in atmospheric CO2. The CO2 increase is driven by emissions of carbon-containing fuels, not by changes in the ozone layer.
Now, consider the answer choices as a whole: A choice asserting that II., III and IV are true would misstate IV, since IV is false. A choice listing I., II., III. and IV would include I and IV, both of which are incorrect. A choice of I. and III. omits II, which is true. The only option that correctly pairs the true statements II and III is the one that states II. and III.
Therefore, the option containing only II. and III. captures the accurate combination of true statements among I–IV.

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