修改下列病句。    
1．印刷术是中国古代的四大发明。
                                                                                                             
2．夏天的天气又炎热又凉爽。
                                                                                                             
3．我怀着愉快而高兴的心情，接受了任务。 
                                                                                                             
4．电灯是爱迪生发现的。