【单选题】On the one hand, the spammers on social media can be a high risk towards the security of legitimate users and on the other hand some of the legitimate users, such as bloggers can pollute the _________...
【简答题】A.Finding the true nature of subatoraic particles. B.Their work on very high frequency radio waves. C.Laying the foundations of modern mathematics. D.Their discovery of the laws of cause and effect.