18330. They have built a perfect dam across the river.
Across the river a perfect dam was built.
A perfect dam has been built by them across the river.
A perfect dam should have been built by them.
Across the river was a perfect dam.
ব্যাখ্যা: Present perfect tense যুক্ত বাক্যকে passive করতে হলে structure হবে object কে sub + have/has been + verb-এর p.p + by + sub কে ob + extension, সুতরাং সঠিক উত্তর b