单选题
When an organism is completely encapsulated and preserved, it becomes a fossil,
therefore
turning into evidence of things that once lived.
【正确答案】
A
【答案解析】[解析] 本题考查副词应用。Therefore和thereby均为副词，表“因此”，但therefore后通常跟一个句子，而thereby后常接现在分词作状语。as a result of“由于”不符合语境；so也表“因此”，后面也是接句子。因此，答案是A。