小题1:B
小题2:A
小题3:C
小题4:A
一个小小的行动会有很大的影响。
小题1:细节题。根据第三段第1,2行I was riding with my dad to Shreveport for the auction when he found a hitchhiker（搭车者）with a backpack.
小题2:细节题。根据第三段第五行he told dad a lot of terrible things that had occurred to him.
小题3:细节题。根据第三段5,6行I sat in the back seat and watched the scene with amazement.中的with amazement可知我很惊讶。
小题4:推理题。根据倒数第2段第三行Just one single kind act can change someone’s life.可知A正确。