Select the most appropriate option to fill in blank 5.
Show answer & explanation
Correct answer: D
Explanation
The correct answer is option 4 i.e. has been witnessed.
The sentence discusses a notable increase in cyberattacks that has been observed over the duration of the Covid pandemic. "Has been witnessed" effectively communicates that this observation is ongoing and spans the entire period of the pandemic.
Using "has been witnessed" indicates that the increase in cyberattacks started in the past (during the pandemic) and continues to be relevant up to the present, reflecting a long-term trend.