What is the best way to combine Sentences 14 and 15? 1: I thought about napkins for a long time I could not come up with something magnificent.

2: I thought about napkins for a long time, and I could not come up with something magnificent.

3: I thought about napkins for a long time, so I could not come up with something magnificent.

4: I thought about napkins for a long time, but I could not come up with something magnificent.