The development of innovation.1. the storage.2. do not place down stairs.3. not suitable for use in areas where the surface is not smooth like the ground.
Things to development of innovation 1. Not available in store 2. unfit to up - down 3. Not suitable for use in areas where the uneven surface such as the ground.
What to develop innovative 1. Also inconvenient to store 2. Is not suitable to up - down 3. Not suitable for use in the rough surface. Such as the ground