--I will go to Beijing for a visit with my family during the long holiday of May.-.A. S

问题补充：

--I will go to Beijing for a visit with my family during the long holiday of May. ---.

A. So do I.

B. So I do .

C. So will I .

D. So I will.

答案：

A. So do I.

B. So I do .

(答案→)C. So will I .

D. So I will.

解析：根据时态一致原则排除AB选项，so I will 表示强调或重复，so will I 表示我也会……，所以正确答案为C。