Selected information for Teck Resources Limited for the most recent three years is as follows:

Instructions
(a) What was the main driver of the company's return on assets over the last three years? Explain.
(b) What was the main driver of the company's return on common shareholders' equity over the last three years? Explain.

2012 2011 2010 Return on common shareholders' equity Return on assets Debt to total assets Asset turnover Profit margin 4.6% 2.5% 28.6% 0.3 times 8.4% 15.8% 7.2% 28.6% 0.3 times 24.0% 12.2% 6.3% 23.7% 0.3 times 21.1%