by design

副词 by design:

1. with intention; in an intentional manner
   同义词：intentionally, deliberately, designedly, on purpose, purposely, advisedly, by choice

1. I don't know whether they did it by accident or by design.
   我不知道他们这样做是偶然的，还是故意的。
2. He made that remark by design.
   他故意那样说。