某工厂化验室用40g 10%的氢氧化钠溶液中和100g石油产品中残余的硫酸，此时溶液pH=7．求石油产品中H₂SO₄的质量分数是多少？

情景对话

A：Would you like to have dinner with me this evening, Bob? 

B： ____ . Maybe another time.

A：What are you doing?

B：I'm making aplan____

A：What plan? Is it very important?

B：Yes, I always do volunteer work on the first Saturday of every month.

A：____

B：I help out at the children's hospital. I help to plan some activities.

A：____

B：Of course. You should help to make the sick children happy.

A：____ I can tell them some interesting stories.

a. Oh, I'd love to do that.

b. I must finish it on time.

c. Sorry, I can't. I'm busy.

d. Err…Bob, could I join you?

 e. What kind of volunteer work do you do？