问题补充：
My brother is writing a letter to his friend now (用tonight)
答案：
My brother will write a letter to his friend tonight
======以下答案可供参考======
供参考答案1:
My brother is going to write a letter to his friend tonight.
供参考答案2:
my brother is tonight writing a letter to his friend now
供参考答案3:
My brother will writ a letter to his friend tonight.
