中文摘要：

考虑平面上由两个齐次多项式的和所定义的微分系统，并且假设原点是这类微分系统的孤立退化奇点，给出了这类系统的奇点是单值的一个充分必要条件，它推广了文献[1]中的相应结论。

英文摘要：

A class of planar differential systems defined by the sum of two homogeneous polynomials is considered. In our discussion, the origin is assumed to be an isolated and degenerated singular point for these differential systems. A necessary and sufficient condition of a focus-center singular point is given. This result generalizes the corresponding result in [1].