[单选题]诊断的步骤包括( )。
A.要确定运行状态检测的内容、建立测试系统
B.特征提取
C.制定决策
D.要确定运行状态检测的内容、建立测试系统,特征提取,制定决策都正确

As the Internet has rapidly become a mainstream medium, the social impact of the Internet has been a topic of ongoing debate. Some studies have found that Internet use is associated with reduced social networks and increased loneliness.
Internet use appears to cause a decline in psychological well-being, {{U}} (31) {{/U}} to research at Carnegie Mellon University. Even people {{U}} (32) {{/U}} spent just a few hours a week {{U}} (33) {{/U}} the Internet experienced more depression and loneliness {{U}} (34) {{/U}} those who logged on less frequently, the two-year study showed. And it wasn’t {{U}} (35) {{/U}} people who were already feeling had spent more time on the internet, {{U}} (36) {{/U}} that using the Net actually appeared to {{U}} (37) {{/U}} the bad feelings.
Researchers are puzzling over the results, {{U}} (38) {{/U}} were completely contrary {{U}} (39) {{/U}} their expectation. They expected that the Net would {{U}}