请找出李阳在学习中的困难。

Dear friend,

      Now I am new here. I have learned English for only one year, so I can't understand what the teacher

says and I am afraid of talking with any classmates in English. I know this is the most important year for

me and I really work very hard. But the biggest problem for me is that I can't read fast and I couldn't sleep

the night before big exams. Could you help me?

                                                                                                                                         Yours,

                                                                                                                                        Li Yang 

1. He can't               __________________

2. He is afraid of       __________________

3. He can't               __________________

4. He couldn't           __________________

下列物质是按氯元素的化合价规律排列的，KCl、（  ）、HClO、KClO₃、HClO₄，则空格内的物质是 [ ]

A．NaCl

B．NaClO

C．Cl₂

D．HClO₃