Plot more curves in one graph

Question

I would like to plot more curves in one window , I want to see superposing those curves.. Concretely plot RHO_start for 3 curves in one window. I don´t know how to write in my code. Here is it:

var projecten = new ol.layer.Group({

            title: 'Projecten',
            layers: [

                new ol.layer.Vector({
                title: 'EVZ Den Dungen',
                source: new ol.source.GeoJSON(
                            /** @type {olx.source.GeoJSONOptions} */ ({
                              object: EVZDenDungen,
                              projection: 'EPSG:3857'
                        })),
                style: function(feature, resolution) {
                    return lookup[feature.get('landschapselement')];
                }
                }),

                new ol.layer.Vector({
                title: 'EVZ Croy',
                source: new ol.source.GeoJSON(
                            /** @type {olx.source.GeoJSONOptions} */ ({
                              object: EVZCroy,
                              projection: 'EPSG:3857'
                        })),
                style: function(feature, resolution) {
                    return lookup[feature.get('landschapselement')];
                }
                }),

                new ol.layer.Vector({
                title: 'Natuurcompensatie Gasselsbroek',
                source: new ol.source.GeoJSON(
                            /** @type {olx.source.GeoJSONOptions} */ ({
                              object: NatuurcompensatieGasselsbroek,
                              projection: 'EPSG:3857'
                        })),
                style: function(feature, resolution) {
                    return lookup[feature.get('landschapselement')];
                }
                }),

                new ol.layer.Vector({
                title: 'Ebben',
                source: new ol.source.GeoJSON(
                            /** @type {olx.source.GeoJSONOptions} */ ({
                              object: Ebben,
                              projection: 'EPSG:3857'
                        })),
                style: function(feature, resolution) {
                    return lookup[feature.get('landschapselement')];
                }
                }),

                new ol.layer.Vector({
                title: 'Zionsburg',
                source: new ol.source.GeoJSON(
                            /** @type {olx.source.GeoJSONOptions} */ ({
                              object: Zionsburg,
                              projection: 'EPSG:3857'
                        })),
                style: function(feature, resolution) {
                    return lookup[feature.get('landschapselement')];
                }
                })


            ]
})