A：How's business?
生意如何?
B：Couldn't be better.
好得不得了。
注释：
(It) Couldn't be better.
(好得不得了/好得不能再好了。)
*此处couldn't 不可用can't代替。
例：A: How're you doing?
(A：近来如何?)
B: Couldn't be better.
(B：好得不得了。)