老少爺們copy吧，最好自己敲一遍

var image = ee.ImageCollection('COPERNICUS/S2_SR')

???????.filterDate('2020-01-01','2020-12-31')

???????.filter(ee.Filter.lt('CLOUDY_PIXEL_PERCENTAGE',10))

???????.filterBounds(roi)

???????.median()

???????

//set visualization parameter for sentinel 2A image

var visParamsTrue = {bands:['B4','B3','B2'],min:0,max:2500,gamma:1.1};

Map.addLayer(image,visParamsTrue,"sentinel 2A");

var studyarea = image.clip(roi);

Map.addLayer(studyarea,visParamsTrue,"studyarea");

????

//export to drive

????

Export.image.toDrive({

image:studyarea.int16(),

description:'xining',

scale:10,

region:roi,

maxPixels:1e13

});