The correct answer is: B. Pamela said that she had given the packet to Tom,who kept it a long time.
The sentence “I gave the packet to Tom,who kept it a long time,” said Pamela. is in the past tense. This means that Pamela is talking about something that happened in the past. The verb “gave” is in the past tense, and the word “who” is used to introduce a clause that describes Tom. The clause “who kept it a long time” is a relative clause, and it tells us that Tom kept the packet for a long time.
The other options are incorrect because they do not agree with the tense of the sentence. Option A is incorrect because the verb “had gave” is in the past perfect tense, which is used to talk about something that happened before another event in the past. Option C is incorrect because the word “for” is used to introduce a duration of time, and the sentence does not need a duration of time. Option D is incorrect because the word “to” is used to introduce a purpose, and the sentence does not need a purpose.