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With most of the focus being placed on the carbon cycle, the effects of human use of nitrogen often slip under the radar. It is estimated that agriculture may be responsible for half of the nitrogen fixation on earth, primarily through the use and production of man-made fertilizers. Excess levels of nitrogen in water can cause issues in marine ecosystems, primarily through overstimulation of plant and algae growth. This can result in blocked intakes and less light getting to deeper waters, damaging the rest of the marine population.

Paul and Oliver often have picnics in the picnic area in summer.
Paul and Oliver usually play sports at the sports center on holiday.
Paul sometimes watches birds in the Wales parks in August.
Paul and Oliver always have countryside walks in the Wales parks at weekends.
Oliver often rides a bike in the Wales parks in summer.
Paul sometimes rides a horse  in the Wales parks on holiday.
Paul and Oliver usually fish in the Wales parks every summer.
Oliver often climbs mountains in the Wales parks in summer.
Paul and Oliver sometimes buy souvenirs in the Wales parks on holiday.

Christmas is(тк he, she, it – is, а в нашем случае Christmas - "it")  my favourite holiday. We are(тк we, you, they-are, а в нашем случае "we") at home. We have(тк we, you, they-have got, а в нашем случае "we") got a beautiful Christmas tree. The house is (тк he, she, it – is, а в нашем случае house-"it") clean and tidy. Before the Christmas my mum and dad go to( тк "to" обозначает направление действия) the shop. Then mum cooks(тк это Present Simple, а в этом времени мы к he, she, it добавляем "s", то есть как бы заменяем "does") Christmas dinner. We help her(тк he "он"-him "ему", а she "она"-her "ей"). I set ( lay- положить, а set-накрывать) the table. In the afternoon we sit down at the table (здесь я не нашла ошибку). Our pets are (тк we, you, they-are, а в нашем случае pets-"they")  with us too. After dinner my brother washes (тк это Present Simple, а в этом времени мы к he, she, it добавляем "s", то есть как бы заменяем "does") the dishes.