The correct answer is A. laughed.
The sentence is in the past tense, so the verb must also be in the past tense. The other options are not in the past tense.
A. laughed is the simple past tense of the verb to laugh. It means that someone did laugh at the funny situation.
B. has laughed is the present perfect tense of the verb to laugh. It means that someone has laughed at the funny situation at some point in the past.
C. will laugh is the future tense of the verb to laugh. It means that someone will laugh at the funny situation at some point in the future.
D. has been laughing is the present perfect continuous tense of the verb to laugh. It means that someone has been laughing at the funny situation for some period of time.
In this case, the best option is A. laughed because it is the only option that is in the past tense.