Tobacco mosaic and Turnip mosaic are both viral diseases that affect plants, while Late blight of potato is a fungal disease. However, both tobacco mosaic and turnip mosaic can have similar symptoms and are caused by viruses. Therefore, the correct answer is option 'D' - both (a) and (c).

1. Tobacco Mosaic:
- Tobacco mosaic is a viral disease that affects various plants, including tobacco, tomatoes, peppers, and other solanaceous plants.
- It is caused by the Tobacco mosaic virus (TMV), which is transmitted through infected plant debris, mechanical transmission (such as by hands or tools), or by sap-sucking insects.
- The virus causes distinct mosaic-like patterns on the leaves, with light and dark green areas alternating, giving a mosaic appearance.
- Other symptoms include stunted growth, leaf distortion, and reduced yield in affected plants.
- TMV can persist in plant debris for long periods and can be easily spread through handling or contact with infected plants.

2. Turnip Mosaic:
- Turnip mosaic is also a viral disease that affects various plants, including turnips, radishes, and other cruciferous vegetables.
- It is caused by the Turnip mosaic virus (TuMV), which is transmitted through aphids and infected seed.
- The virus causes mosaic symptoms on the leaves, with light and dark green patches, as well as yellowing and distortion.
- Infected plants may also show stunted growth, reduced yield, and deformed fruits.
- TuMV can persist in infected plant debris and can be spread by aphids, which feed on infected plants and then transmit the virus to healthy ones.

3. Late Blight of Potato:
- Late blight of potato is a fungal disease caused by the pathogen Phytophthora infestans.
- This disease is specific to potatoes and tomatoes and can cause significant damage to the crops.
- Late blight can spread rapidly in cool and humid conditions, infecting leaves, stems, and tubers.
- Infected plants show water-soaked lesions on leaves, which later turn brown and necrotic.
- The disease can also affect the tubers, causing rotting and decay.
- Late blight is primarily spread through spores that are produced on infected plant parts and can be carried by wind or water.

In conclusion, both tobacco mosaic and turnip mosaic are viral diseases caused by different viruses, while late blight of potato is a fungal disease. Therefore, the correct answer is option 'D' - both (a) and (c).