What prevents the blood from flowing backwards

A set of valves exist between each atrium and ventricle, preventing blood from flowing backwards into the atria. 

Schools are being forced to embrace computers. unlike their "digital immigrant" teachers, these students are "digital natives", born into a world where technology is an integral part of everyday life. almost every student has access to a multitude of computers, laptops and tablet devices. it would be crazy to assume an assignment would  notbe written on computer in this day and age.many schools now have a 1-to-1 computer policy, and many districts and states in the united states have mandated computers or ipads across the state for every student,  including los angeles, the second largest school district in the country.but the thing is, when they tried it in la, it wasn't the success they hoped for. that's because the tablets weren't used as much as they expected. rather, it appeared there was a gap between the digital native's love of technology and their use of it in the classroom.this conflicted relationship with computers is also underscored by much of the literature on education. it is also highlighted in professional development and conferences such as  edutech.