Which of the following affects the surfaces of historical buildings made out of sandstone or limestone, and causes a reaction that forms a powdery substance that can be washed away by rain?
coal dustsulfur pollutantsvolcanic ashnone of these were mentioned in the reading

answer; i believe the correct answer is (a) nigeria is the largest african crude (oil) supplier; /// so revenue from petroleum;

d. new methods of assembly are introduced.

explanation:

this allows for the goods to be made on a larger scale. not faster because now it is shown to be made better, hence the greater productivity in the question. it is calling for something new to be introduced.