Correct Answer: March

Solution : May's percentage drop = $\frac{450 – 400}{450}\times 100=11.11$%
April's percentage drop = $\frac{200 – 180}{200}\times 100=10$%
March's percentage rise = $\frac{240 – 110}{110}\times 100=118.18$%
February's percentage reduction = $\frac{350 – 300}{350}\times 100=14.28$%
January's percentage rise = $\frac{230 – 220}{220}\times 100=4.54$%
Thus, the maximum growth occurred in March, the month which shows the highest growth will have the largest ratio.
Hence, the correct answer is March.