Please explain this SAT grammar to me!

<p>The illustrated books by Dr. Suess HAVE managed KEEPING youngsters and adults ALIKE entertained FOR several decades. NO ERROR</p>

<p>"keeping" should be "to keep"
I can see how "to keep" sounds better, but what is the grammatical reason "to keep" works instead of "keeping?"
I thought keeping could be the direct object (managed what? managed keeping.) Why is that wrong?</p>

<p>WHEN he suggested TO BUILD the United States Capitol AT THE CENTER OF Washington D.C., he also OFFERED to design a landscaped mall nearby. NO ERROR</p>

<p>Here, "to build" is suppose to be "building"</p>

<p>Whats the difference between these two examples?</p>

<p>This question gets asked quite frequently on CC, and I always refer people to [url=<a href="http://grammar.ccc.commnet.edu/grammar/gerunds.htm%5Dthis%5B/url"&gt;http://grammar.ccc.commnet.edu/grammar/gerunds.htm]this[/url&lt;/a&gt;], in which the rules for choosing between gerund and infinitive complements are delineated.</p>