Okay, of course it's a simple sentence, but if we're talking about more complex sentences and there is no hierarchy between the words, it's really hard to get your point.
If a second language learner has a classroom teacher who talks in the target language at a quicker rate, in complex sentences, and about complicated matters, the learner will probably have a harder time in the learning process.
And then of course remember you want to be mixing complex and simple sentences and you're building them up like you're building a house and you could then get something like this.
Now that could be because it uses a lot of high vocabulary and complex sentences, or it could be that the emotional content of the book is difficult to read.
One tip to build your reading skills, which will also help you answer sentence simplification questions, is to look at complex sentences or paragraphs, and separate the main ideas from less important information.