Funding for this research was provided by:
Natural Science Foundation of Guangxi Province (2015GXNSFAA139185)
Received: 18 November 2019
Accepted: 22 January 2020
First Online: 30 January 2020
Ethics approval and consent to participate
: Not applicable.
: All authors agreed on the final approval of the version to be published. All authors agree to be accountable for all aspects of the work in ensuring that questions related to the accuracy or integrity of any part of the work are appropriately investigated and resolved.
: The authors declare that they have no competing interests.