Expected behavior Select menu should display when click

Actual behavior When clicking on Select, nothing happens. No menu shown.

Resources (screenshots, code snippets etc.)

      <MDBSelect>
              <MDBSelectInput selected="Choose your country" />
              <MDBSelectOptions>
                <MDBSelectOption disabled>
                  Choose your country
                </MDBSelectOption>
                <MDBSelectOption value="1">1</MDBSelectOption>
                <MDBSelectOption value="2">2</MDBSelectOption>
                <MDBSelectOption value="3">3</MDBSelectOption>
                <MDBSelectOption value="4">4</MDBSelectOption>
              </MDBSelectOptions>
            </MDBSelect>