The key word of this sentence is “while”, it’s normally used to described an ON-GOING action. You click it?? On-going action refers to “-ing” , doesn’t it? Only answer fits!
“d” having being as –ing form is a correct answer. “a” is passive form of past tense, and “c” is passive form, but it is a present perfect tense.
I hope this is another “a piece of cake” for you.