Virtualbox android virtual machine how to access the folder on the host machine?

I have installed an android virtual machine in Virtualbox on my Ubuntu 16.04 host machine.

And I have set the Network as Host-only Adapter.

And here it is the shared folder:I can't access the shared folder in android virtual machine.

And I the IP address of the android virtual machine is 192.168.56.101. And adb connect 192.168.56.101 has successfully connected.
I have tried ES file explorer, but I don't how it can access the shared folder in my host machine.

So I want to know how I can access the host machine folders in android virutal machine. Is there any way? Thanks.

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