第 4 题
若有如下程序段，其中 s、a、b、c 均已定义为整型变量，且 a、c 均已赋值（c>0）
<div data-v-ce91c296="" class="jsk-code-block no-selection jsk-code-block-copy-show" style="border-color: rgb(221, 221, 221); width: inherit;"><div data-v-ce91c296="" class="vue-codemirror jsk-code-block-codemirror" style="max-height: inherit;"><textarea name="codemirror" placeholder="" style="display: none;"></textarea><div class="CodeMirror cm-s-eclipse CodeMirror-wrap" translate="no" style="clip-path: inset(0px);"><div style="overflow: hidden; position: relative; width: 3px; height: 0px; top: 29.5938px; left: 60.3906px;"><textarea autocorrect="off" autocapitalize="off" spellcheck="false" readonly="" tabindex="0" style="position: absolute; bottom: -1em; padding: 0px; width: 1000px; height: 1em; min-height: 1em; outline: none;"></textarea></div><div class="CodeMirror-vscrollbar" tabindex="-1" cm-not-content="true"><div style="min-width: 1px; height: 0px;"></div></div><div class="CodeMirror-hscrollbar" tabindex="-1" cm-not-content="true"><div style="height: 100%; min-height: 1px; width: 0px;"></div></div><div class="CodeMirror-scrollbar-filler" cm-not-content="true"></div><div class="CodeMirror-gutter-filler" cm-not-content="true"></div><div class="CodeMirror-scroll" tabindex="-1"><div class="CodeMirror-sizer" style="margin-left: 30px; margin-bottom: -17px; border-right-width: 33px; min-height: 59px; padding-right: 0px; padding-bottom: 0px;"><div style="position: relative; top: 0px;"><div class="CodeMirror-lines" role="presentation"><div role="presentation" style="position: relative; outline: none;"><div class="CodeMirror-measure"><pre class="CodeMirror-line-like"><span>xxxxxxxxxx</span></pre><div class="CodeMirror-linenumber CodeMirror-gutter-elt"><div>2</div></div></div><div class="CodeMirror-measure"></div><div style="position: relative; z-index: 1;"></div><div class="CodeMirror-cursors" style="visibility: hidden;"><div class="CodeMirror-cursor" style="left: 30.3906px; top: 25.5938px; height: 25.5938px;"> </div></div><div class="CodeMirror-code" role="presentation"><div style="position: relative;"><div class="CodeMirror-gutter-wrapper" aria-hidden="true" style="left: -30px;"><div class="CodeMirror-linenumber CodeMirror-gutter-elt" style="left: 0px; width: 21px;">1</div></div><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"><span class="cm-variable">s</span> <span class="cm-operator">=</span> <span class="cm-variable">a</span>;</span></pre></div><div style="position: relative;"><div class="CodeMirror-gutter-wrapper" aria-hidden="true" style="left: -30px;"><div class="CodeMirror-linenumber CodeMirror-gutter-elt" style="left: 0px; width: 21px;">2</div></div><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"><span class="cm-keyword">for</span> (<span class="cm-variable">b</span> <span class="cm-operator">=</span> <span class="cm-number">1</span>; <span class="cm-variable">b</span> <span class="cm-operator"><=</span> <span class="cm-variable">c</span>; <span class="cm-variable">b</span><span class="cm-operator">++</span>) <span class="cm-variable">s</span> <span class="cm-operator">=</span> <span class="cm-variable">s</span> <span class="cm-operator">-</span> <span class="cm-number">1</span>;</span></pre></div></div></div></div></div></div><div style="position: absolute; height: 33px; width: 1px; border-bottom: 0px solid transparent; top: 59px;"></div><div class="CodeMirror-gutters" style="left: 0px; height: 92px;"><div class="CodeMirror-gutter CodeMirror-linenumbers" style="width: 29px;"></div></div></div></div></div><div data-v-ce91c296="" class="jsk-code-block-buttons"><!----><!----></div></div>
则与上述程序段功能等价的赋值语句是( )。
s = s - c s = a - c s = b - c s = a - b
