Properties of Series Convergence

Consider the following statements regarding the convergence of infinite series.

I. The series $\sum_{n=1}^\infty \frac{1}{n^2}$ is convergent.

II. The harmonic series $\sum_{n=1}^\infty \frac{1}{n}$ is convergent.

III. The alternating harmonic series $\sum_{n=1}^\infty (-1)^{n+1} \frac{1}{n}$ is conditionally convergent.

Which of the above statements is/are true?