The terms 'WannaCry, Petya and EternalBlue' sometimes mentioned in the news recently are related to

1. A

   Exoplanets

   (a) Exoplanets. Exoplanets are worlds around other stars, named in astronomy news, not in ransomware headlines. WannaCry and Petya are unrelated to that field. This option is not the key.

2. B

   Cryptocurrency

   (b) Cryptocurrency. Some ransomware demanded bitcoin, but EternalBlue is an NSA-leaked SMB exploit and the three names together denote malware campaigns, not a currency. This option is not the key.

3. C

   Cyber attacks

   (c) Cyber attacks. WannaCry (2017) and Petya/NotPetya were ransomware/wiper waves; EternalBlue was the leaked exploit that helped them spread across unpatched Windows SMB. The trio belongs to cyber-attack news. This option is the official key.

4. D

   Mini satellites

   (d) Mini satellites. CubeSats and other small satellites are a space-tech topic, not these names. This option is not the key.

Summary. Official key is (c) Cyber attacks. WannaCry and Petya were 2017 malware outbreaks; EternalBlue was the SMB exploit that enabled rapid worm-like spread. The set is therefore a cyber-security cluster, not exoplanets, crypto as such, or mini satellites. Bitcoin appeared only as a ransom channel in some strains. The stored letter is (c).