Why English is nessesary in present senerio?

Answer 1

Do you mean here on this site? Yahoo's site, so Yahoo sets the rules.

Answer 2

If by the present scenario you mean today's world, I think the answer is that the British created an Empire that spanned the globe. They set up governments and trading companies (some of which acted like governments) all over the place. Most of those colonies have become independent countries, but a great deal of the infrastructure remains, including the language, in places like Hong Kong, India, and East Africa.
Before English became the "lingua franca" of commerce, it was French (still is in diplomatic circles) and before that it was Greek, at least throughout the Mediterranean and Middle East. Spanish still thrives everywhere south of the US (with the notable exception of Brazil, which speaks Portuguese). In Asia, Chinese has long been the language of intercultural trade and diplomacy, and I can easily imagine that if their current growth continues, Chinese will once again become an international language. The current dominance of English is a historical "accident." Whether the reasons for that dominance are judged in the future to have been good or bad is not for me to say, but it is today's reality.