$\begin{array}{l}\text{Here, }\\ \Rightarrow \text{40\% of 250 = 50\% of ?}\\ \\ \text{It can be also written as}\\ \\ \frac{40}{100}\times 250=\frac{50}{100}\times x[\because puttingx=?]\\ \\ \Rightarrow \text{40}\times \text{2.5 =}\frac{1}{2}\times x\\ \\ \Rightarrow x=\text{100}\times \text{2}\\ \\ \Rightarrow x=200\\ \end{array}$

Hence, option A is correct.