根据首字母及句意补全单词  。

1. We should keep c        in front of danger.  

2. Our Chinese teacher is very s         . We are a little afraid of( 害怕)him.  

3. My sister is m        outgoing than me.  

4.  A            they are twins, they look different in some ways.  

5. B          of the twins are funny.

在钻井过程中，油气浸入井筒后，在循环过程中上返，钻井液池面上有气泡、油花等现象叫（）。