You can try to apply for a single entry visa with 90 days stay duration. From the date of issue, a single-entry visa shall be valid for 3 months, duration of each stay is granted on a case by case basis at the discretion of consular officers in accordance with relevant guidelines, If your estimated stay in China is longer than 30 days, please make it clear in the application form and ask for the Visa Officer's approval when you submit your application..