Bicameral Legislature system was introduced for the first time in Pakistan in ___?

Bicameral Legislature system was introduced for the first time in Pakistan in ___?

پاکستان میں پہلی بار دو ایوانی مقننہ کا نظام ___ میں متعارف کرایا گیا؟
Explanation

From 1947 to 1973, Pakistan had a unicameral legislature with only the National Assembly.

The 1973 Constitution introduced a bicameral system, adding the Senate alongside the National Assembly.