diff --git a/MVMCore/MVMCore/OtherHandlers/MVMCoreCache.m b/MVMCore/MVMCore/OtherHandlers/MVMCoreCache.m
index d2c298c..45e9603 100644
--- a/MVMCore/MVMCore/OtherHandlers/MVMCoreCache.m
+++ b/MVMCore/MVMCore/OtherHandlers/MVMCoreCache.m
@@ -513,13 +513,14 @@ static NSString * const STATIC_CACHE_COMPONENT = @"StaticCache.txt";
     });
 }
 
+//download image
 - (void)downloadImage:(NSURL *)s7URL isGif:(BOOL)isGif fallbackImageName:(nullable NSString *)fallbackImageName completionHandler:(nonnull MVMCoreGetImageBlock)completionHandler{
     NSURLCache *sharedCache = [NSURLCache sharedURLCache];
     NSURLSessionConfiguration *configure = [NSURLSessionConfiguration defaultSessionConfiguration];
     configure.URLCache = sharedCache;
     NSURLSession *session = [NSURLSession sessionWithConfiguration:configure];
     NSURLRequest *request = [NSURLRequest requestWithURL:s7URL cachePolicy:NSURLRequestUseProtocolCachePolicy timeoutInterval:ImageTimeOut];
-    
+    //use Freebee to download image first, then store image to cache
     NSCachedURLResponse *cachedResponse = [sharedCache cachedResponseForRequest:request];
     if (!cachedResponse.data) {
         cachedResponse = [[MFFreebeeHandler sharedHandler] freebee_dataWithImageURL:s7URL];
@@ -529,6 +530,7 @@ static NSString * const STATIC_CACHE_COMPONENT = @"StaticCache.txt";
             [sharedCache storeCachedResponse:cachedResponse forRequest:request];
         }
     }
+    //call nsurlsession again, if image is cached by Freebee, the second session will grab image data from cache instead of making another server call
     NSURLSessionDownloadTask *downloadImageTask = [session downloadTaskWithRequest:request completionHandler:^(NSURL * _Nullable location, NSURLResponse * _Nullable response, NSError * _Nullable error) {
         NSData *data = [NSData dataWithContentsOfURL:location];
         NSCachedURLResponse *cachedreponse = [[NSCachedURLResponse alloc] initWithResponse:response data:data];
@@ -547,6 +549,7 @@ static NSString * const STATIC_CACHE_COMPONENT = @"StaticCache.txt";
     [downloadImageTask resume];
 }
 
+//check whehter get image or imageData, if not, return fallbackImage
 - (void)checkImage:(UIImage *)img imageData:(NSData *)imageData fallbackImage:(NSString *)fallbackImageName completionHandler:(nonnull MVMCoreGetImageBlock)completionHandler{
     // Set to the fallback image.
     BOOL isFallBackImage = NO;