The correct answer is E. were killed.
The tomb of the Unknown Soldier is a monument dedicated to the memory of soldiers who have died in war and whose remains have not been identified. People go to the tomb to stand in silence for a minute to honor the memory of those who were killed in wars.
The other options are incorrect because they do not accurately reflect the purpose of the tomb of the Unknown Soldier. Option A, is killed, is incorrect because it implies that the soldiers who are honored at the tomb are still being killed. Option B, will be killed, is incorrect because it implies that the soldiers who are honored at the tomb will be killed in the future. Option C, was killed, is incorrect because it implies that the soldiers who are honored at the tomb were killed at a specific point in time. Option D, are killed, is incorrect because it implies that the soldiers who are honored at the tomb are being killed on a regular basis.