以文本读写方式打开一个已有的文件 file1.txt ,下面有关 fopen 函数正确的调用 _______ 。
A.
FILE *fp ; fp = fopen( "file1.txt" , "r" ) ;
B.
FILE *fp ; fp = fopen( "file1.txt" , "r+" ) ;
C.
FILE *fp ; fp = fopen( "file1.txt" , "rb" ) ;
D.
FILE *fp ; fp = fopen( "file1.txt" , "rb+" ) ;