【单选题】

Do you know that, last year atone, over 20 million cell phone users in this country (145) to switch to newer models

And what did they do with their old ones, you may ask Well, nothing-and that means that (146) phones have now been added to the growing mountain of disused telephones which is currently estimated at something like 66 million. So, if you are planning on changing yours sometime soon, then (147) of simply discarding it, make a gesture for the environment.
Enclosed with this issue of your monthly magazine, you will find a postage-paid envelope that you can use to send your old phone to us. For each phone that our readers send in, we will receive a donation of ￡2.50 from RecyclePhone, (148) is currently the world’s [eading mobile phone recycling company. This money wilt be used to help us to finance our "Be GreenAware" campaign, which we will be launching nationwide in July.
Don’t miss this opportunity to make your contribution to intelligent recycling.
A、that
B、what
C、whose
D、which