i want to prepare for civil services and have completed my 12th from science stream so plz tll me the best field to choose.

if you are asking for best stream for UG, i would say go for some three year course, may be BSc. i mean no need to invest 4 years in BTech. but the above holds only if you are highly enthusiastic to get into civils.

If you want to go for Civil Services then dont prefer Science or Engineering.You better go for Arts it will also help in your entrance exam