fix confusing sentence

initial fragment(s) to the activity during the activity's

{@link android.app.Activity#onCreate onCreate()} method.</p>

<p>An important rule when dealing with fragments&mdash;especially those that you add at

runtime—is that the fragment must have a container {@link android.view.View} in the layout in

which the fragment's layout will reside.</p>

<p>An important rule when dealing with fragments&mdash;especially when adding fragments at

runtime—is that your activity layout must include a container {@link android.view.View}

in which you can insert the fragment.</p>

<p>The following layout is an alternative to the layout shown in the <a

href="creating.html">previous lesson</a> that shows only one fragment at a time. In order to replace