To determine the correct answer, let's first understand the terms monocarpellary, unilocular, and the presence of many ovules.

A monocarpellary ovary is one that is formed from a single carpel. A unilocular ovary means that the ovary develops a single locule or chamber. Having many ovules indicates that numerous ovules are contained within this single locule. Now, let's examine each plant:

Sesbania: Monocarpellary and unilocular with many ovules.

Brinjal (Eggplant): Typically, this has a bicarpellary (two carpels) and bilocular (two chambers) ovary, not fitting the criteria.

Indigofera: Monocarpellary and unilocular with many ovules.

Tobacco: Usually has a bicarpellary and bilocular ovary, so it does not meet the criteria.

Asparagus: It usually has a tricarpellary and trilocular ovary, so it does not fit the criteria.

Based on the above information, the plants that have monocarpellary, unilocular ovaries with many ovules are Sesbania and Indigofera.

Therefore, the correct answer is:

Option D: A and C only