I came to Manchester two weeks ago.I came to Manchester two weeks ago.
I came to Manchester before two weeks.
Use "past time + ago"
10 years ago, a long time ago, a few weeks ago, a couple of days ago
Use "before + action / event"
before you left, before we start, before lunch
2. fall 还是reduce?
These two words are the opposites of 'rise' and 'raise':
something falls (e.g. the price fell)
somebody reduces something (e.g. the company reduced the price)
You will probably use 'fall' to describe numbers on a graph or chart for IELTS Writing Task 1:
In 2008, the number of customers fell. (verb, past)
There was a sharp fall in Internet usage. (noun)
'Reduce' and 'reduction' are probably more useful for Writing Task 2:
We need to reduce the amount of pollution from exhaust fumes. (verb)
Recycling leads to a reduction in waste. (noun)
3. because还是because of?
Compare these two sentences:
I stayed at home because the weather was bad.
I stayed at home because of the bad weather.
The important difference is the use of the word 'was' in the first sentence. After 'because', you need a subject and a verb (e.g. the weather was). After 'because of', we don't use a verb, only a noun, nouns or noun phrase.
重要的区别在于第一句里使用了word。Because后面需要加主语和动词(例如the weather was)。Because of 后面不需要动词，只要一个或多个名词，又或者名词词组就可以了。