A、A more economical diesel run. B、Characteristics of a new type of run. C、Where a new energy source is located. D、How to develop

W：Hello? May I speak to Bill Johns?
M：Hi，Amy．This is Bill．
W：Oh，hi，Bill．You weren’t in engineering class today，were you?
M：No，I wasn’t．(20)I have a flu．I was wondering if you could tell me what went on．
W：I’m sorry that you are ill．Actually we had an interesting class。(19)Dr．Collin talked about a new type of fuel．
M：Oh, yeah? Tell me more about it．
W：Uh hum．It’s called DME．
M：Oh．I remember reading something about DME．It’s mostly used in spray cans，right?
W：Right．DME doesn’t destroy the ozone，so it’s been environmentally friendly．
M：But doesn’t DME pollute the air if it’s burned in an engine?
W：Dr．Collin says something about its exhausts being clear，that it doesn’t release as much pollutants as diesel fuel．He mentioned something about DME being more efficient than other alternative fuels．
M：When will it replace diesel fuel?
W：Not for a while．It’s not economical to mass produce．But it may happen in the future．After all，time will tell．
M：Well，thanks for the information．(21)I guess I won’t need to borrow your notes．
W：(21)Well，maybe you should look at them．We are having a test next week．You have to prepare for it．
M：Okay，could you give them to Mike Andrews? I think he is in your psychology class．He is my roommate．
W：Sure．I hope you’re feeling better soon．
M：Thanks．Me too．Bye!