Plantation agriculture is a type of commercial farming system characterized by large-scale production of cash crops such as tea, coffee, rubber, sugarcane, etc. It is typically practiced in tropical and subtropical regions where the climate and soil conditions are favorable for the cultivation of these crops. The following characteristics define plantation agriculture:

Large capital investments:
- Plantation agriculture requires significant capital investments to establish and maintain large estates or plantations.
- This includes the purchase or lease of land, infrastructure development, purchase of machinery and equipment, and other operational expenses.
- The scale of production and the need for efficient organization and management necessitate substantial financial resources.

Scientific methods of cultivation:
- Plantation agriculture relies on the application of scientific methods of cultivation to maximize crop yields and quality.
- This includes the use of modern agricultural practices such as soil testing, crop rotation, irrigation, fertilization, pest and disease control, and mechanization.
- Scientific knowledge and research are essential to optimize production and ensure the sustainability of the plantation.

Multi-crop specialization:
- Plantations typically focus on the cultivation of a single cash crop or a limited number of crops.
- This specialization allows for economies of scale, efficient production, and market dominance in specific crop sectors.
- Some examples of multi-crop specialization in plantation agriculture include tea plantations, coffee plantations, and rubber plantations.

Highly-paid skilled workforce:
- Plantation agriculture requires a skilled and specialized workforce to carry out various tasks such as planting, harvesting, processing, and maintenance.
- Workers in plantations are often well-paid compared to other agricultural sectors due to the technical nature of the work and the need for expertise.
- Skilled workers are essential for the efficient operation of plantations and the implementation of scientific cultivation practices.

Based on the given characteristics, the correct answer is option B: 1 and 3 only. Plantation agriculture involves large capital investments and the use of scientific methods of cultivation. It does not necessarily require multi-crop specialization or a highly-paid skilled workforce, although these factors are often associated with plantation agriculture.