已知Service通信的代码，以下哪些语句会阻塞? server.cpp int main(int argc, char **argv) {

已知Service通信的代码，以下哪些语句会阻塞？ server.cpp int main(int argc, char **argv) { ros::init(argc, argv, "greetings_server"); //① ros::NodeHandle nh; //② ros::ServiceServer service = nh.advertiseService("greetings", handle_function);//③ ros::spin(); //④ return 0; } client.cpp int main(int argc, char **argv) { ros::init(argc, argv, "greetings_client"); ros::NodeHandle nh; ros::ServiceClient client = nh.serviceClient﹤service_demo::Greeting﹥("greetings"); //⑥ service_demo::Greeting srv; srv.request.name = "HAN"; srv.request.age = 20; if (client.call(srv)) //⑦ { .... } return 0; }()。

A、①

B、②

C、③

D、④

E、⑤

F、⑥

G、⑦