题目

After my mother passed away，my dad tried even harder to stay healthy and active.Each morning he swam in the pool，and no matter how he felt，he would __36__swim one more lap(圈) than the previous day，just to prove there was always room for __37__. By his late 70s，in spite of his swimming，his strength and energy had noticeably __38__.By age 81，he was in poor health because of heart problems and arthritis(关节炎)．He pretended he didn’t__39__to lean heavily on me for support as we walked slowly；I pretended not to __40__，and naturally held him.One day he said，“IAmerican college students are increasingly        with credit card debt and the consequences can be rather serious.A.boostedB.burdenedC.substitutedD.dominated