If $a_k$ is an increasing function of $k$, i.e. $a_1<a_2<\ldots<a_k \ldots$. Then which of the following is $\text{TRUE.}$
- $\lim _{n \rightarrow \infty} \sum_{k=1}^{n} \frac{1}{a_{k}}=\infty$.
- $\lim _{n \rightarrow \infty} \sum_{k=1}^{n} \frac{1}{\left|a_{k}\right|}<\infty$.
- Either $(a)$ or $(b)$.
- $\lim _{n \rightarrow \infty} \sum_{k=1}^{n} \frac{1}{a_{k}}=0$.
- None of the above.