why your play in 1.e4 e5?

I like do it

Why post in this thread then?

The key thing if you're going to play 1.e4 e5 (which I do) is to be prepared for:

1. Kings's Gambit: 1.e4 e5  2.f4
2. Scotch Game: 1.e4 e5 2.Nf3 Nc6 3.d4
3. Italian Game: 1.e4 e5 2.Nf3 Nc6 3.Bc4
4. Spanish Game: 1.e4 e5 2.Nf3 Nc6 3.Bb5

There are others but the above should cover 90+ percent of what you need to know

Well, I don't tend to. I have nearly 1300 games in the Sicilian as black and 72 games playing 1. e4 e5 as black. In general I feel 1. e4 e5 is basically saying to your opponent "break me down, I dare you", trying to make white prove an advantage, while 1. e4 c5 is basically like "you might have the advantage to start with, but you better not misstep". Seems more aggressive. (of course, I'm sure many masters would tell me I'm talking crap, but whatever. I have a winning record with the Sicilian as black and a losing record with it as white, with 1. e4 e5 I have the more conventional winning record as white and losing record as black. 

Don't forget about the Danish Gambit.

One way to sidestep the main lines of the Danish is with 1.e4 e5 2.d4 exd4 3.c3 Qe7 -- every time I've ever played this White starts burning clock, because he is totally unprepared

1.e4 e5 2.d4 exd4 3.c3 d5 and danish gambit goes nowhere...

Also there's the Latvian Gambit, but I rarely ever play that since it's a rather specific line for black in order to use it effectively.

That assumes you play 2...Nc6.

Nothing wrong with that move, I've played it probably about 30 to 50 times in my 2500 game career (over the board), but I've also played maybe 20 to 30 games with 2...Nf6!

If you go the route of the Petroff, it does shorten the list of what you have to know.  It removes all of the 2.Nf3 Nc6 items, like the Scotch, Ruy Lopez, etc., and limits it to:

1.King's Gambit

2.Danish (which as previously mentioned, is garbage, just play 3...d5, which then avoids the Goring Gambit too!)

3.Center Game

4.Petroff

one of the most cowardish opening I know, played by some of the worst cowards on the planet

Those that think the Petroff is a Coward's opening don't understand the Petroff even one iota!

The Petroff can be a very wild game, and I've had many.

Also, I dare you to walk up to Kramnik, Anand, and Carlsen, and tell them all that they are cowards!  They all have played the Petroff as Black in their careers!  Look at the world championship match between Carlsen and Anand - BOTH of them played it as Black!

I'm saying it is played by some people for the wrong reasons.

That's what I say about the London System, especially those that have no clue when to use it!

It's not a catch-all opening by any stretch, and while many GMs have proven this already, London guru Cyrus Lakdawala even admits himself that the London System is no good against the Modern Defense!  Black gets in e5 way too quickly, and White's Bishop bites on granite for life!  He's virtually playing down a piece!

Look, avoiding theory and enhancing theory in your own little universe is not exactly the same thing. Also claiming someone has been using an engine when investigating new roads is cowardice par excellence from someone leaving the engine on, the appropriate nucleus word is probably on stand by, past a certain move, in their beloved Petroff.

As black,I answer 1.e4 with e5 because I want my opponent to play his favorite opening;then,I wil try and win anyway.I do the same when playing black vs 1.d4.

Uhhh.... In what way is the Petrov cowardish? There's a ton of variety there.

 I quite like playing the Jaenisch (3 ... f5) against the Ruy Lopez. You have to assume your opponent will play the Ruy Lopez though. 3... f5 isn't that great against Giuoco Piano (Italian) as the bishop on c4 makes it hard to castle, and white gets good play with 4. d4. I still played it in my current daily chess game though (when my opponent played 4. d3 which is also a reasonable move).

It is easier to play chess with the aid of an engine ( I know the kind, I know for sure ), it is not much of a problem if you can somewhat shorten the number of lines you need to learn, the Petroff is perfect.