We need to evaluate each expression using the order of operations (BODMAS/PEMDAS):

1. Expression A: $20 - 5 \times 2 + 4$ $20 - 10 + 4$ (Multiplication first) $10 + 4$ (Subtraction then Addition from left to right) $= 14$ (Not 10)

2. Expression B: $(15 - 5) \times 2 \div 2$ $10 \times 2 \div 2$ (Brackets first) $20 \div 2$ (Multiplication then Division from left to right) $= 10$ (This is 10)

3. Expression C: $30 \div (2 + 3) \times 1$ $30 \div 5 \times 1$ (Brackets first) $6 \times 1$ (Division then Multiplication from left to right) $= 6$ (Not 10)

4. Expression D: $40 \div 8 + 3 \times 2$ $5 + 6$ (Division and Multiplication first) $= 11$ (Not 10)

Therefore, only expression B simplifies to 10.