What is the word "trouble" in the second paragraph referring to? ( )

(单选题)Readers can find answers to the following question except ( (单选题)Which of the following statement is not true? ( ) (单选题)What makes this study different from previous research which (单选题)The author writes the first para.in order to ( ) (单选题)Which factor cannot result in dog’s stress? ( ) (单选题)According to the article, which one of the following stateme (单选题)“Don't sleep easy yet, though”, because ( ). (单选题)What does the underlined word "skimpy" in the third paragrap (单选题)According to the Fed, ( ) (单选题)What can we infer from the first paragraph? ( )