Question

1) India has been an independent country since/for ...
1945; the end of World War II; the last five decades; more than 50 years.
2) Our company has sold 50 types of new goods since/for
1993,last year, six months, twenty-four weeks, the beginning of the year 2001, the new mashines were bought , two year

Answer 1

1) India has been an independent country 
since 1945;
since  the end of World War II;
for the last five decades;
for more than 50 years.

2) Our company has sold 50 types of new goods

since 1993,
since last year,
for six months,
for twenty-four weeks,
since the beginning of the year 2001,
since the new machines were bought ,
for two years