A structural adaptation is defined as the adaptation in which physical features of organisms or plants while behavioral adaptation is defined as the activities an organism or plant do to survive.
The Himalayan balsam plant is an example of behavioral adaptation because it disperse its seeds when it ripe and touched by someone, for its survival it shows it dispersal behavior and spread seeds as far as 16 feet from the parent plant. In the fear of someone can harm by touching it, the survival instinct of balsam plant shows behavioral adaptation.
Hence, the correct answer is " behavioral adaptation".
To give an analogy of an atom; If the whole atom was a large football stadium then the nucleus would be a soccer ball at the center of the pitch in the stadium, with electrons (that hold negligible mass) skimming about in the empty space. This center ball carried most of the mass of the atom. Therefore most matter that you see is actually and ironically empty space.
