What causes acidification of rain and what is the main effect of the acidification on crops?

Influence of aluminum on the uptake of various cations from a solution into carrots
Read the article and answer the following questions:
What causes acidification of rain and what is the main effect of the acidification on crops?
Provide name of all elements that were utilized for preparation of multitracer solution.
Above what Al concentration was the deformation of carrot roots observed? At what AlCl3 concentration was the rate of cerium uptake into intact roots the highest? What is the pattern in uptake rate for rear earth elements?
What is the reported influence of Al3+ on the uptake of beryllium, strontium and barium by a carrot roots? What is responsible for this uptake?
Compare uptake of manganese, cobalt and zinc into roots and leaves at 0.002 ppm of Al.
Answers to all questions must be typed.
NOTE: You may need to find secondary sources to answer question 1. In such case, you must cite your sources at the end of the assignment, following the examples below. Remember that reproducing text from a source verbatim is plagiarism, and such incidences can become part of your academic record.
How to cite a web page:
National Library of Medicine. Environmental Health and Toxicology: Specialized Information Services. http://sis.nlm.nih.gov/enviro.html (accessed Aug 23, 2004).
How to cite a scientific journal article:
Evans, D. A.; Fitch, D. M.; Smith, T. E.; Cee, V. J. Application of Complex Aldol Reactions to the Total Synthesis of Phorboxazole B. J. Am. Chem. Soc. 2000, 122, 10033-10046.