“Cell phone” is a     American usage，but British speakers always use “mobile phone”．

You are _____ careful than your brother. You two can’t do the work that needs care and skill.  

You can never be ________ when crossing the street. 

Professor White has written some short stories, but he is _____ known for his plays. 

---Look, our headmaster is over there, playing basketball with some students of our class. --- Oh, he must be ________ to his students.