Legislation was introduced in 1987 to ban the use of compounds that were depleting the ozone layer. The graph below shows the levels of halogens in the atmosphere for several years after the legislation was passed.

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What conclusion can you draw from this graph?

A. The size of the ozone layer decreased during this time period.
B. The concentration of ozone in the upper atmosphere increased during this time period.
C. The concentration of halogens in the atmosphere decreased during this time period.