D. The Present Continuous is formed from the present tense of the verb be and the present participle '-ing' form of a verb: 'am/ is/ are + ~ing'
a. I am doing something = I'm in the middle of doing it: I've started doing it and I haven't finished yet. (e.g. Please don't make so much noise. I'm trying to work. (not I try))
b. The action is not necessarily happening at the time of speaking. (e.g. I'm reading a really good book at the moment. I'm not reading the book at the time of speaking. I mean that I have started it, but have not finished it yet. I am in the middle of reading it)
c. Some friends of mine are building their own house. They hope to finish it next summer.
d. Verbs are not normally used in the Present continuous: like, love, hate, need, prefer, know, realise, suppose, mean, understand, believe, remember, belong, fit, contain, consist, seem, etc.
D1. We use the Present Continuous tense to talk about the present:
a. that is happening at the moment of speaking. (e.g. I’m just leaving work. I’ll be home in an hour.)
b. which is happening before and after a given time. (e.g. At eight o’clock we are usually having breakfast.)
c. which we think is temporary. (e.g. Michael is at university. He’s studying history.)
d. which is new and contrasts with a previous state. (e.g. These days most people are using email instead of writing letters.)
e. to show that something is changing, growing or developing: get, change, become, increase, rise, fall, grow, improve, begin, start. (e.g. The children are growing quickly.)
f. for something which happens again and again. (e.g. It’s always raining in London.)
D2. We use the Present Continuous tense to talk about the future: for something which has been arranged or planned. (e.g. Mary is going to a new school next term.)
D3. We can use the Present Continuous to talk about the past. (e.g. When we are telling a story)
Idiom 365
Costs an Arm and a Leg: a lot of money or extremely expensive
Example: I tried to find out the designer bag for my daughter's gift. It cost me an arm and a leg though!