If you want to improve your muscular strength what is the best plan

The best plan is: high resistance low reps

Explanation:

Weight training is a strength training that consists of lifting weights, either with dumbbells or specific devices. Its goal is to promote muscle strength and muscle atrophy. It is important that the individual who wants to do weight training gets in contact with a professional to seek guidance, but we can say that if he wants to improve his muscle strength, the ideal is that he practice high resistance low reps.

However, the good execution of the exercises and some tricks make the difference to obtain better results. And so, it explains why your friend, who started exercising at the same time as you, already has a much more defined body.

d would be your answer