**6. Conclusions**

We have introduced the latest progress in controllability of stochastic linear systems and put forward some problems that need to be further studied, which includes stochastic linear systems in finite dimensional spaces, stochastic linear systems in infinite dimensional spaces, stochastic singular linear systems in finite dimensional spaces, and stochastic singular linear systems in infinite dimensional spaces. The controllability and observability for a type of time-varying stochastic singular linear systems have been studied by using stochastic GE-evolution operator in the sense of mild solution in Banach spaces, some necessary and sufficient conditions have been obtained, the dual principle has been proved to be true, an example has been given to illustrate the validity of the theoretical results obtained in this part. Readers can easily and comprehensively understand the latest progress concerning the controllability of stochastic linear systems and further problems to be solved. The next research direction is how to solve these problems.

**Funding:** This research was funded by National Natural Science Foundation of China grant numbers 12126401 and 11926402.

**Institutional Review Board Statement:** Not applicable.

**Informed Consent Statement:** Not applicable.

**Data Availability Statement:** Not applicable.

**Acknowledgments:** The author would like to thank the anonymous reviewers and the Editor for their helpful comments.

**Conflicts of Interest:** The author declares no conflict of interest.
