There is the question 8 of my 10 questions. Thank you.

8. Which of the following differential two forms can be written as do) for some one form a)? If the answer is yes, nd such a one form w. (a) :cdy A dz + (a: z)dz A dm | zdm A dy, (b) mdy A dz + (a: z)dz A dz; + zdm A dy, (o) 2yzdy A dz + 3x2zdz A dz; + sale: A dy