To solve this problem, we need to identify which plant has diadelphous stamens.$\newline$Let's analyze the options:$\newline \bullet$China rose:$\newline$ - China rose, or Hibiscus rosa-sinensis, has monadelphous stamens.$\newline$ - In monadelphous stamens, all stamens are united into a single bundle by their filaments.$\newline \bullet$Citrus:$\newline$ - Citrus plants typically have polyadelphous stamens.$\newline$ - In polyadelphous stamens, stamens are united into more than two bundles.$\newline \bullet$Pea:$\newline$ - Pea plants, or Pisum sativum, have diadelphous stamens.$\newline$ - In diadelphous stamens, the stamens are united into two bundles.$\newline$ - Typically, in pea plants, nine stamens are fused together, and one stamen is free, forming two groups.$\newline \bullet$China rose and citrus:$\newline$ - As discussed, China rose has monadelphous stamens, and citrus has polyadelphous stamens.$\newline$Therefore, the correct answer is Option 3: Pea, which has diadelphous stamens.