How to know the "id responseObject" is an NSArray or an NSDictionary using AFNetworking

I'm using Objective-C and AFNetworking. I made a post request and it will retu a JSON string. I can get an NSDictionary like this:{msg="...", result="..."}, or an NSArray like this:{{id=1, content="..."},{id=2,content="..."}...}. So here's the thing: further tasks I need to do will differ according to the JSON String I get.

How do I make the code tell whether the type of the JSON string is NSArray or NSDictionary?

Here is my code:

AFHTTPSessionManager *manager = [AFHTTPSessionManager manager];
manager.responseSerializer.acceptableContentTypes = [NSSet setWithObject:@"text/html"];

[manager POST:url parameters:parameter progress:nil success:^(NSURLSessionDataTask *task, id responseObject) {
    if (responseObject is an NSDictionary){
        //do something
    }
    else{
        //do something
    }
}failure:^(NSURLSessionDataTask *task, NSError *error) {
    NSLog(@"Error: %@", error);
}];

Thanks in advance!