You would say ‘There was a blackfin in the water' . One thing you made clear about confusing prepositions that thoseare confusing for all. Okay, here's another really common fixed expression. A lot of thanks to you.I have learnt many things from your English Grammar- Preposition lesson.But please clearly differentiate”By” as you have done already about”IN, ON, AT”. There’s a lot of writing on the Internet, our blog included. Here are some sentences that people wrote below Thursday's writing task 1 lesson. Then come back and read it again. 1. So, the "cost of oil" tends to refer to production costs, rather than the price for the buyer. So in all of these examples, the preposition “at” is used to talk about specific places or points in space. It's an enclosed room or enclosed space. 4.Oil and food prices show similar patterns over the period. With lots of good wishes. If you missed it, you can watch it up here. There's no simple rule, there's no one answer. Or both are correct? These little words can cause lots of headaches if English is not your first language. Rio | Thank you for all of them. Now it's also used with public places and shops. Oil and food prices followED nearly THE same trends within THE REPORTED period. Thanking you in anticipation. Prepositions must be learned in chunks of words or called collocations – groups of words that are often used together. Are there any important differences between the following sentences?