The method is as follows:
1. Hold your nostrils with your fingers (usually thumb and forefinger) to ensure that the nasal cavity cannot breathe.
2. Try to pronounce な. If your fingers feel vibration, your voice becomes deep (just like talking to the mouth of a jar), and your pronunciation is correct.
2. Try to pronounce. If you pronounce correctly, your fingers won't feel vibration and your voice won't be affected in any way.
3. Practice the other pseudonyms of these two lines repeatedly.
This method was used by myself in those years, because when I read individual sounds, I was used to nasal sounds, that is, the sounds of the な line, especially ぬ and る, and I couldn't tell them apart at all. I have to concentrate on the front and read the back easily. Once the teacher asked me to read it seven times in a row in class, and finally even the teacher gave up. But after using this method, I quickly grasped the difference between the two. In fact, you can also understand the difference by practicing Chinese such as "there" and "to get milk".