使用C语言编写一个程序，输入两个英文句子，每个句子里英文单词之间用空格分隔，输出它们最长的公共单词。

您好！您可以使用C语言编写一个程序来实现这个功能。以下是一个示例程序：

#include <stdio.h>
#include <string.h>

#define MAX_LENGTH 100

void findCommonWord(char* sentence1, char* sentence2, char* result) {
    char* word1 = strtok(sentence1, " ");
    char* longestCommonWord = "";

    while (word1 != NULL) {
        char* word2 = strtok(sentence2, " ");
        
        while (word2 != NULL) {
            if (strcmp(word1, word2) == 0 && strlen(word1) > strlen(longestCommonWord)) {
                longestCommonWord = word1;
            }
            
            word2 = strtok(NULL, " ");
        }
        
        word1 = strtok(NULL, " ");
    }

    strcpy(result, longestCommonWord);
}

int main() {
    char sentence1[MAX_LENGTH];
    char sentence2[MAX_LENGTH];
    char commonWord[MAX_LENGTH];

    printf("Enter the first sentence: ");
    fgets(sentence1, sizeof(sentence1), stdin);
    sentence1[strcspn(sentence1, "\n")] = '\0';

    printf("Enter the second sentence: ");
    fgets(sentence2, sizeof(sentence2), stdin);
    sentence2[strcspn(sentence2, "\n")] = '\0';

    findCommonWord(sentence1, sentence2, commonWord);

    if (strlen(commonWord) > 0) {
        printf("The longest common word is: %s\n", commonWord);
    } else {
        printf("No common word found.\n");
    }

    return 0;
}

这个程序使用了`strtok`函数来将句子拆分成单词，并使用`strcmp`函数来比较两个单词是否相等。最长的公共单词是通过比较单词长度来确定的。