It’s an error quite common among schools.
This flower is common in spring.
2) ordinary 指符合壹般或常規事物標準或相同的規格，因而只具有普通的特性。例如：
Although he is rich, he is always in ordinary dress.
common與ordinary基本同義，強調“平凡的，普通的”，表示隨時可以碰到，不值得驚奇。如：
an ordinary ( a common) event 常有的事情
an ordinary (a common0 person 壹個普通的人
3) normal 表示“正常的，常態的，正規的”，相對於非正常而言。例如：
Do you know the normal temperature of the human body.
His growth is normal for that age.
4) usual 通常與人的行為習慣有關，含義為“慣常的，通例的”。例如：
Tea is considered to be the usual drink of British people.
He arrived later than usual.
Common 用於是通常的、常發生的、廣泛使用或眾所周知的：
a common problem;
***同的問題；
a common thief;
普通的小偷；
the common dandelion. The term also suggests lack of distinction and can imply coarseness or crudeness:
普通的蒲公英。 此詞條也暗示缺乏區別並能意指粗劣或未加工：
drank wine of the commonest sort;
最為普遍的飲用葡萄酒；
had a very common look about him.
他有著很普通的外表。
Ordinary
describes what is of the usual kind and is not distinguished in any way
from others. In the latter sense it is sometimes derogatory:
Ordinary 指種類普通且不能從其他中加以區別的。在後壹意義上，它有時是貶義的：
A ballpoint pen is adequate for most ordinary purposes.
原珠筆適合最普通的用途。
The violinist gave a very ordinary performance marked by an occasional memory lapse.
小提琴手因偶然記憶失誤表現很平常。
Normal stresses adherence to an established standard, model, or pattern:
Normal 強調符合已建立的標準、模型或方式：
normal body temperature;
正常體溫；
normal curiosity.
正常的好奇心。