Which of the following pairs of animal phyla are the most closely related

There are three phyla that categorizes worms which are platyhelminthes (flatworms), nematodes (round worms) and annelids (segmented worms).In this case, the pair that is closely related is C. annelids and flatworms since they are both worms

Description of  thigmotropism is given below.

Explanation:

1. Thigmotropism is a plant’s response to touch.It is a plant’s response to an external stimulus.It can occur quickly or slowly.Thigmotropism may involve the closing and opening of plant leaves.

2. Thigmonasty or thigmotropism can be define as the response of touch shown by the plants. Here, touch is the external stimulus. It can be define as the movement of the plant parts in response to the external stimulus that is contact or touch. It is also known as Haptotropism. The plant may change it's orientation, shape and size of the plant parts.

3,The thigmotropism can be positive or negative depending upon the visual response shown by the plants. The response shown by the plants is generally fast  but may be slow. This response is shown by the plants in cases of danger of herbivory.Some plants like Mimosa pudica or touch me not plant shows thigmotropism by closing their leaves on touch