Shrubs are a type of plant that have certain distinct features. Among the given options, option A, "Short and busy stem," is the correct answer.

Shrubs have short and busy stems, which means that their main stems are relatively short and give rise to numerous branches. These branches often grow close together, creating a dense and compact appearance.

Here is a detailed explanation of the features of shrubs:

1. Short and busy stem:
- Shrubs typically have a main stem that is relatively short compared to trees.
- The short stem gives rise to multiple branches, creating a bushy and compact growth habit.
- This characteristic makes shrubs suitable for hedging, bordering, or filling in gaps in a garden or landscape.

2. Long branches (not a feature of shrubs):
- Long branches are not a typical feature of shrubs.
- While shrubs may have branches, they are generally shorter in length compared to the branches of trees.
- Trees, on the other hand, are characterized by their long and often tall branches.

3. Weak stem (not a feature of shrubs):
- Shrubs do not have weak stems.
- While the stems of shrubs may not be as strong or sturdy as those of trees, they are still capable of supporting the weight of the branches and leaves.
- Weak stems are more commonly associated with herbaceous plants or certain types of climbers.

In conclusion, the correct feature of shrubs among the given options is a short and busy stem (option A). Shrubs are characterized by their compact growth habit, with a relatively short main stem giving rise to numerous branches.