Which one of the following statements is true about "grandfather paradox"?
选项：

A:

When you traveled back into the past, you would have no chance to encounter the "grandfather paradox".

B:

One could simply avoid the "grandfather paradox" by leaving their grandfather alive.

C:

One could simply avoid the "grandfather paradox" by killing their grandfather.

D:

No one could avoid the "grandfather paradox" if they travel into the past.