Mobile phone slogans are not allowed here.

Test analysis: At normal temperature, gasoline is easy to vaporize, and the air around the gas station is full of gasoline vapor. If there is an open flame, it is easy to cause an explosion. Therefore, gas stations have slogans such as "Please turn off the gas and refuel" and "Please don't use your mobile phone".

So choose a.

Comments: This question mainly examines students' understanding of vaporization and explains some phenomena in life with vaporization knowledge.