Same reasons as why people feel differently toward real life. It depends on your activities on Internet, and the kind of environment you spent in it, mainly how other users interacted you.
        
             
        
        
        
2**(32 - netmask) - 2 = number of nodes available
The netmask is in CIDR (Common Internet Domain Routing) notation, without the slash.
One of the nodes would be needed for a router or else you can't communicate with other networks.
        
             
        
        
        
Answer: (D) Distributed denial- of- service (DDoS)
Explanation:
 The distributed denial of service attack is one of the type of attack that occur when the multiple system are basically flooded with the resources and the bandwidth. 
- Botnet is one of the example of DDoS as it caused the DOS (denial of service) for the users.
- This type of attack is more substantial as compared to the DoS attack as they use the multiple system for attack the single target simultaneously.
Therefore, Option (D) is correct.