2. In each of the following groups of words, there are four underlined letters or letter combinations marked A, B, C and D. Compare the underlined parts and identify the one that is different from the others in pronunciation.
A、there
B、thick
C、thank
D、thirty
How does exercise sharpen the mind according to Para.2?
A、By increasing the brain siz
B、By decreasing the protein level.
C、By extending the time of concentration.
D、By strengthening brain cells’ connections.
Which of the following is closest in meaning to “sitting on the sidelines” in Para. 3?