To answer this question, we need to recall the specific details from the Valentine's Day episode in season 6 of Friends. In this episode, Chandler gives Monica a mix tape with Janice's voice on it. Let's go through each option to identify the two songs that Janice is singing:
Option A) I'll Be There For You & My Funny Valentine - This option is incorrect because "I'll Be There For You" is the theme song of Friends, not a song that Janice sings on the mix tape.
Option B) Celebration & I'll Be There For You - This option is incorrect because, as mentioned before, "I'll Be There For You" is not one of the songs Janice sings.
Option C) Celebration & The Way You Look Tonight - This option is incorrect because Janice does not sing "The Way You Look Tonight" on the mix tape.
Option D) The Way You Look Tonight & My Funny Valentine - This option is correct. Janice sings "The Way You Look Tonight" and "My Funny Valentine" on the mix tape.
Therefore, the correct answer is option D.