<aura:component controller="ApexController">
    <aura:attribute name="dataList1" type="String[]" default="[]"/>
    <aura:attribute name="dataList2" type="String[]" default="[]"/>

    <aura:handler name="init" value="{! this }" action="{! c.onInit }" />

    <lightning:select aura:id="select1" label="Select 1" >
        <aura:iteration items="{! v.dataList1 }" var="item">
            <option text="{! item }" value="{! item }" />
        </aura:iteration>
    </lightning:select>

    <lightning:select aura:id="select2" label="Select 2" >
        <aura:iteration items="{! v.dataList2 }" var="item">
            <option text="{! item }" value="{! item }" />
        </aura:iteration>
    </lightning:select>
</aura:component>

({
    onInit: function(component, event, helper) {
        helper.loadDataForSelect1(component);
        helper.loadDataForSelect2(component);
    },
});

({
    loadDataForSelect1: function(component) {
        const action = component.get("c.getdData1");
        action.setCallback(this, function(response) {
            const state = response.getState();
            if (state === "SUCCESS") {
                component.set("v.dataList1", response.getReturnValue());
            } else {
                let errors = response.getError();
                let message = 'Unknown error'; // Default error message
                // Retrieve the error message sent by the server
                if (errors && Array.isArray(errors) && errors.length > 0) {
                    message = errors[0].message;
                }
                // Display the message
                console.error(message);
            }
        });

        $A.enqueueAction(action);
    },
    loadDataForSelect2: function(component) {
        const action = component.get("c.getdData2");
        action.setCallback(this, function(response) {
            const state = response.getState();
            if (state === "SUCCESS") {
                component.set("v.dataList2", response.getReturnValue());
            } else {
                let errors = response.getError();
                let message = 'Unknown error'; // Default error message
                // Retrieve the error message sent by the server
                if (errors && Array.isArray(errors) && errors.length > 0) {
                    message = errors[0].message;
                }
                // Display the message
                console.error(message);
            }
        });

        $A.enqueueAction(action);
    }
})

public with sharing class ApexController
{
    @AuraEnabled
    public static List<String> getdData1()
    {
        return new List<String> {'One', 'Two', 'Three'};
    }

    @AuraEnabled
    public static List<String> getdData2()
    {
        return new List<String> {'Red', 'Green', 'Blue'};
    }
}