Create a sequential list with some data elements, and finish such operations as initialization, insertion, deletion etc. all operations should be implemented as independent functions, which can be called by the main function. (1) create a sequential list with data elements of 21, 18, 30, 75, 42, 56, and output all the elements (2) get the 3rd element of the list, and output the value; (3) insert 67 into the list at positon 3, and then output all the elements in the list;