Which of the following integrals is unbounded ?

• A. \(\mathop \smallint \limits_0^{\frac{\pi }{4}} \tan xdx\)
• B. \(\mathop \smallint \limits_0^\infty \frac{1}{{{x^2} + 1}}dx\)
• C. \(\mathop \smallint \limits_0^\infty x{e^{ - x}}dx\)
• D. \(\mathop \smallint \limits_0^1 \frac{1}{{1 - x}}dx\)