In a leaf, what is the outer layer of the vein composed of?

The outer layer of the vein is made of cells called bundle sheath cells (E), and they create a circle around the xylem and the phloem.

sulfur dioxide

explanation: acid rain is caused by a chemical reaction that begins when compounds like sulfur dioxide and nitrogen oxides are released into the air. these substances can rise very high into the atmosphere, where they mix and react with water, oxygen, and other chemicals to form more acidic pollutants, known as acid rain.

answer; the tunica intima also called tunica interna, consists of elastic fibers,connective tissue and smooth muscle cells;