Option 1 states that both Statement I and Statement II are true, and Statement II is the correct explanation of Statement I.

Statement I claims that the growth of plants is smooth with a complete fertilizer. This means that using a complete fertilizer provides the necessary nutrients for plants, leading to healthy and steady growth.

Statement II states that a complete fertilizer always contains N, P, K. N stands for nitrogen, P stands for phosphorus, and K stands for potassium. These are three essential nutrients for plant growth. Nitrogen helps with leaf and stem growth, phosphorus aids in root development and flowering, and potassium contributes to overall plant health. A complete fertilizer with these elements ensures that plants receive the necessary nutrients for optimal growth.

Option 1 suggests that both statements are individually true, and Statement II is the correct explanation of Statement I. This means that using a complete fertilizer with N, P, K indeed leads to smooth plant growth because it provides the necessary nutrients for healthy development. Therefore, Option 1 is the correct answer.