diff --git a/thu_os/answers.md b/thu_os/answers.md
new file mode 100644
index 0000000..3569820
--- /dev/null
+++ b/thu_os/answers.md
@@ -0,0 +1,5 @@
+操作系统错题答案
+==============
+
+1. C
+<br/>分页方式不会有外碎片
diff --git a/thu_os/mistakes.html b/thu_os/mistakes.html
new file mode 100644
index 0000000..a129cea
--- /dev/null
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+  margin: 10px 0;
+  height: 24px;
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+  -moz-border-radius: 3px;
+  border-radius: 3px;
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+  text-decoration: line-through;
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+  -moz-osx-font-smoothing: grayscale;
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+@media print {
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+  .markdown-body {
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+  .markdown-body a,
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+  .markdown-body .headeranchor-link {
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+  .markdown-body pre {
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+  .markdown-body pre,
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+  .markdown-body .progress,
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+    box-shadow: none;
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+  .markdown-body .progress {
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+  .markdown-body .progress-bar {
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+  .markdown-body tr,
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+  .markdown-body img {
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+  .markdown-body h2,
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+.codehilite .gc{color:#999;background-color:#EAF2F5}
+</style><title>mistakes</title></head><body><article class="markdown-body"><h1 id="_1">操作系统错题<a class="headerlink" href="#_1" title="Permanent link"></a></h1>
+<ol>
+<li>在使能分页机制的情况下，更合适的外碎片整理方法是（）\
+    A. 紧凑(compaction)
+    B. 分区对换(swapping in/out)
+    C. 都不是</li>
+</ol></article></body></html>
\ No newline at end of file
diff --git a/thu_os/mistakes.md b/thu_os/mistakes.md
new file mode 100644
index 0000000..015232a
--- /dev/null
+++ b/thu_os/mistakes.md
@@ -0,0 +1,7 @@
+操作系统错题
+===========
+
+1. 在使能分页机制的情况下，更合适的外碎片整理方法是（）
+	+ 紧凑(compaction)
+	+ 分区对换(swapping in/out)
+	+ 都不是
