GWD6-29

Q29:

Prospecting for gold during the California gold rush was a relatively easy task, because of erosion, prehistoric glacier movement, and ancient, gold-bearing riverbeds thrust to the surface by volcanic activity put gold literally within reach for anybody with a pan or shovel.

1. because of erosion, prehistoric glacier movement, and ancient, gold-bearing riverbeds thrust to the surface by volcanic activity put gold literally within reach for

2. because of erosion, prehistoric glacier movement, and volcanic activity that thrust ancient, gold-bearing riverbeds to the surface, and putting gold literally within reach of

3. owing to erosion, prehistoric glacier movement, and volcanic activity that had thrust ancient, gold-bearing riverbeds to the surface, and putting gold literally within reach of

4. since erosion, prehistoric glacier movement, and volcanic activity that thrust ancient, gold-bearing riverbeds to the surface, putting gold literally within reach for

5. since erosion, prehistoric glacier movement, and ancient, gold-bearing riverbeds thrust to the surface by volcanic activity put gold literally within reach of

   Answer: E

借这个题问一下because of和since的区别？