In deciding on a research topic, what questions may we ask ourselves to check the availability of the required sources? ( )
选项：

A:What kind of participants/subjects do I have to invite to participate in my research? Where can I find them? Will they accept my invitation?
B:Do I have to use questionnaires? How many people will be willing to respond to my questionnaire? Who are they?
C:Do I need to interview some of the participants? Are they available for the interviews I plan to conduct? When and where can I carry out the interviews?
D:Can I find the necessary materials and information in my school and local libraries? If not, can I request them by mail or through an interlibrary loan?