a tentative smile的用法和样例：
- With a tentative smile, the man with the guitar turned to me and asked me to accompany him on my harmonica.
- They set up a tent near the seashore.
- We rigged up a tent with an old blanket.
- Here is a tentative free on board price list.
- She rose and took a tentative step backward.
- What is a tentative advertising appropriation ?