Answer, d, C.

The first problem is that the area enclosed by f(x) and X axis is a positive number.

But the integral of f(x). So add the absolute value.

The second question, I integrand function is odd function, and the integral value is 0.

The x part of j integrand function is odd function.

The first half of k integrand function is odd function, and the second half is even function and > 0.

Extended data:

Since the establishment of calculus system for hundreds of years, great achievements have been made in the application of methods. However, there are many imperfections and inaccuracies in the current calculus principle. This is not only because:

1, the current calculus principle cannot be justified in structure;

2. There are many subtle problems;

There are many logical errors in this calculus principle. Moreover, it is also because this calculus principle can hardly play the role of principle. Therefore, it is an insurmountable step in the development of mathematics to correct the mistakes of the current calculus principle, establish a new mathematical model and rebuild the new calculus principle that meets the requirements of mathematical development.