The troposphere part of our atmosphere contains most of tthe weather activity like clouds, rain and snow.
The troposphere is the lowest part of our atmosphere. It is the part where we live on earth.
The altitude of the troposphere is ranges from 8 km to 15 km.
This part also contain most the water vapour.
Thus, the layer A contains the most water vapour and weather activity.
Hence, the option A is the correct answer.