I really can’t express my idea in English freely in-deed. 我确实不能用英语流利地表达我的思想。 (表示某种语言用in)
I wrote a novel in Russian. 我用俄语写了一本小说。(同上)
The kilometer is the biggest unit of length in the metric system. 公里是米制中最长的长度单位。 (表示度、量、衡单位的用in )
The length is measured in meter,kilometre,and centimetre. 长度是以米、公里、厘米为单位来计算的。(同上)
This board was cast in bronze not in gold. 这个牌匾是铜铸的,不是金铸的。