尽管他已经20岁了，但他幼稚的行为举止还是显得很不成熟。

Despite being 20 years old, his ___immature behavior still shows a lack of maturity.

这只小鸟羽毛还没长齐，看起来还很幼小。

The baby bird looks ___immature with its feathers not fully grown.

农民担心霜冻会导致果实过早成熟。

The farmers feared frost would cause ___premature ripening of the fruits.