the newly built building is about ________A 30 metres high B 30-metre-high C 30-metre high

答案应该是A。提供几个例句如下供你参考：
The highboard are 3 metres, 5 metres, 7.5 metres, and 10 metres high. 跳台分3米、5米、7.5米和10米高的跳台。
The water tower is fifty metres high. 这个水塔上下有50米。
That building must measure at least 30 metres. 那座楼至少有30米高。
The building over there is about 230 metres high. 这幢楼有230米高。
The springboards are 1 metre and 3 metres high. 跳板的高度是1米和3米。
That hill is a bout eight hundred metres high. 那小山约有800米高。
I am 30 years old. 我三十岁了。
Built in 1950, the bridge is 30 years old.这座桥是1950年修的，已经有30年历史了。
One is less than 1.1 meters, the other is 1.2 meters tall. 一个不到一米一，另一个身高一米二。
Goliath was a fearless warrior over three meters tall. 身高超过三公尺的歌利亚，是一位天不怕地不怕的勇士。
Mugsy is a real shrimp -- only 1.6 meters tall. 马格西博格体格实在是矮小，身高只有一米六。
如果能帮到你就请采纳。
祝你进步，新年快乐！

带杠不带S，带S不带杠哦……所以A和B都可以

A 参考 I am 15-year-old.或者 I am 15 years old 格式