设变量已正确定义,为了检查以下else-if语句的分支是否正确,至少需要设计( )组测试用例。 if(op == '+'){ printf("=%.2f\n", value1 + value2); }else if(op == '-'){ printf("=%.2f\n", value1 - value2); }else if(op == '*'){ printf("=%.2f\n", value1 * value2); }else if(op == '/'){ if(value2 != 0){ printf("=%.2f\n", value1 / value2); }else{ printf("Divisor can not be 0!\n"); } }else{ printf("Unknown operator!\n"); } A. 7 B. 6 C. 5 D. 4