you just need to provide the following documents for L visa application:
1.A valid passport as well as a copy of its information page: Your valid passport must have at least six (6) months of remaining validity and at least one blank visa page in it.
2.Application form: One completed Visa Application Form. please write that your planned stay duration in China in 90 days on the visa application form.
3.Photo: one recent photo of 2x2 square inch (black & white or color is acceptable) glued or stapled on the application form.
4. your can provide the returned flight tickets to prove your planned 90 days stay duration.

Visa Officers are empowered to make final decision on the validity,duration of stay and times of entry of a visa and may require the applicants provide relevant documents.