1. Correct Answer: Option B: 12 minutes
 2. Explanation:
     To solve this problem, we need to determine the combined rate at which both pipes A and B fill the tank and then calculate the time it takes for them to fill the tank together.
     Step 1: Determine the rate of each pipe.
         ○ Pipe A can fill the tank in 20 minutes. Therefore, the rate of Pipe A is:
       \[
       \text{Rate of Pipe A} = \frac{1}{20} \text{ of the tank per minute}
       \]
         ○ Pipe B can fill the tank in 30 minutes. Therefore, the rate of Pipe B is:
       \[
       \text{Rate of Pipe B} = \frac{1}{30} \text{ of the tank per minute}
       \]
     Step 2: Determine the combined rate of both pipes.
     When both pipes are opened simultaneously, their rates add up. Therefore, the combined rate is:
     \[
     \text{Combined Rate} = \frac{1}{20} + \frac{1}{30}
     \]
     To add these fractions, find a common denominator. The least common multiple of 20 and 30 is 60.
     \[
     \frac{1}{20} = \frac{3}{60} \quad \text{and} \quad \frac{1}{30} = \frac{2}{60}
     \]
     Adding these gives:
     \[
     \text{Combined Rate} = \frac{3}{60} + \frac{2}{60} = \frac{5}{60} = \frac{1}{12}
     \]
     Step 3: Calculate the time taken to fill the tank.
     The combined rate of \(\frac{1}{12}\) means that both pipes together fill \(\frac{1}{12}\) of the tank in one minute. Therefore, to fill the entire tank, it will take:
     \[
     \text{Time} = 12 \text{ minutes}
     \]
     Thus, the correct answer is Option B: 12 minutes.