In Ethereum How Is the Block Difficulty Determined in Ethereum

Multiple Choice

In Ethereum how is the block difficulty determined in Ethereum?

A) The Block Difficulty increases when the time between mined blocks is below 10 seconds, while it decreases when the time is above 20 seconds.
B) The Block Difficulty is determined by the Ethereum Committee every fortnight to reflect the average amount of transaction and it cannot be influenced by the network itself.
C) The Block Difficulty increases when the time between mined blocks is below 20 seconds, while it decreases when the tie is above 60 seconds.