diff --git a/paste.c b/paste.c
index f5eaf11..2f594df 100644
--- a/paste.c
+++ b/paste.c
@@ -1,6 +1,8 @@
 #include <stdio.h>
 #include <stdlib.h>
 #include <string.h>
+#include <getopt.h>
+#include <stdbool.h>
 /**
  * Uso: paste [OPÇÃO]... [ARQUIVO]...
  * Escreve linhas constituídas das linhas sequencialmente correspondentes de
@@ -20,40 +22,105 @@
  * Documentação completa em <https://www.gnu.org/software/coreutils/paste>
  * ou disponível localmente via: info "(coreutils) paste invocation"
  */
-
-int main(int argc, char **argv) {
-    int i;
-    FILE **files = malloc((argc - 1) * sizeof(FILE *));
-    char *eofcur = malloc(argc * sizeof(char *));
-    char *eofend = malloc(argc * sizeof(char *));
-    for (i = 0; i < argc-1; i++) {
-        if (strcmp(argv[i+1], "-") == 0)
-            files[i] = stdin;
-        else
-            files[i] = fopen(argv[i+1], "r");
-        eofcur[i] = '0';
-        eofend[i] = '1';
+FILE *openstream(FILE *file, char *str) {
+    file = stdin;
+    if (strcmp(str, "-") != 0)
+        file = fopen(str, "r");
+    if (!file) {
+        perror(str);
+        exit(EXIT_FAILURE);
     }
-    char sep = '\t';
+    return file;
+}
+
+int is_endoffiles(char *list) {
+    for (int i = 0; list[i] != '\0'; i++) {
+        if (list[i] == '0')
+            return 0;
+    }
+    // str = "111111...";
+    return 1;
+}
+
+/**
+ * Abertura de arquivos em paralelo
+ */
+int print_parallel(char **flist, int argc, char sep) {
+    int i;
     char buffer[BUFSIZ];
-    while (strcmp(eofcur, eofend) != 0) {
-        for (i = 0; i < argc-1; i++) {
+    FILE **files = malloc(argc * sizeof(FILE *));
+    /**
+     * eofstr = "000000..." (args)
+     */
+    char *eofstr = malloc((argc + 1) * sizeof(char *));
+    for (i = 0; i < argc; i++) {
+        files[i] = openstream(files[i], flist[i]);
+        eofstr[i] = '0';
+    }
+    while (!is_endoffiles(eofstr)) {
+        for (i = 0; i < argc; i++) {
             if (fgets(buffer, BUFSIZ, files[i]) == NULL) {
                 strcpy(buffer, "\n");
                 // buffer[0] = '\n';
                 // buffer[1] = '\0';
-                eofcur[i] = '1';
-                if (strcmp(eofcur, eofend) == 0)
+                eofstr[i] = '1';
+                if (is_endoffiles(eofstr))
                     continue;
             }
-            if (i < argc-2)
+            if (i < argc-1)
                 buffer[strcspn(buffer, "\n")] = sep;
             printf("%s", buffer);
         }
     }
-    for (i = 0; i < argc-1; i++) {
+    for (i = 0; i < argc; i++) {
         fclose(files[i]);
     }
     return EXIT_SUCCESS;
 }
 
+/**
+ * Abertura de arquivos serial
+ */
+int print_serial(char **flist, int argc, char sep) {
+    char buffer[BUFSIZ];
+    for (int i = 0; i < argc; i++) {
+        FILE *stream = openstream(stream, flist[i]);
+        while (fgets(buffer, BUFSIZ, stream) != NULL) {
+            buffer[strcspn(buffer, "\n")] = sep;
+            printf("%s", buffer);
+        }
+        putchar('\n');
+        fclose(stream);
+    }
+    return EXIT_SUCCESS;
+}
+
+int main(int argc, char **argv) {
+    int opt;
+    char sep = '\t';
+    bool mode_serial = false;
+    while ((opt = getopt(argc, argv, "d:s")) != -1) {
+        if (opt == 0) {
+            continue;
+        }
+        switch (opt) {
+            case 'd':
+                sep = optarg[0];
+                optind++;
+                break;
+            case 's':
+                mode_serial = true;
+                break;
+            default:
+                abort();
+        }
+    }
+    optind--;
+    if (mode_serial) {
+        print_serial(argv + optind, argc - optind, sep);
+        return EXIT_SUCCESS;
+    }
+
+    print_parallel(argv + optind, argc - optind, sep);
+    return EXIT_SUCCESS;
+}