< b="" />Introduction< />
In this question, we are asked to identify what can alone kill a tree out of the given options. Let's analyze each option to understand why the correct answer is option 'D' - none of the above.

< b="" />Analysis< />
< b="" />a) Hacking< />
Hacking is a method of cutting into the tree trunk or branches, usually with an axe or a similar tool. While hacking can cause damage to a tree, it alone may not necessarily kill it. Trees have the ability to heal themselves by forming callus tissue over the wounded area. If the hacking is not severe and the tree is healthy, it can recover from the damage.

< b="" />b) Chopping< />
Chopping refers to the act of cutting down a tree completely. While chopping may result in the death of a tree, it does not represent a situation where the tree is killed alone. Chopping requires external intervention and it is not a natural process that kills a tree by itself.

< b="" />c) Hacking and Chopping< />
Combining hacking and chopping together does not change the fact that chopping is required to kill a tree. Therefore, this option also does not represent a situation where a tree is killed alone.

< b="" />d) None of the above< />
The correct answer is option 'D' - none of the above, as hacking or chopping alone cannot solely kill a tree. Trees are resilient organisms and have various defense mechanisms to protect themselves from external threats. While severe hacking or complete chopping can severely damage or kill a tree, it would still require additional factors such as diseases, pests, environmental changes, or a combination of these to completely kill a tree.

< b="" />Conclusion< />
In conclusion, hacking or chopping alone cannot kill a tree. Trees are able to heal themselves to some extent and have natural defense mechanisms. While severe hacking or complete chopping can certainly cause damage or lead to the death of a tree, it would still require additional factors for the tree to be killed alone.