A City University professor reported that he discovers a vaccine that has been 80 percent effective in reducing the instances of tooth decay among small children." Here which of the underlying word is incorrect?

Sentence improvement.
Soon after the Tsunami had killed thousands of people along the coast, the Parliament passes a bill that proposed to set up an instituional mechanism to respond promptly to natural disasters.

Identify the grammatical error: 'Hardly had he arrived when the storm has begun.'

Scarcely $\frac{had he reached}{A}$ the airport $\frac{when}{B}$ the announcement $\frac{was made}{C}$ that the flight $\frac{has been}{D}$ cancelled.

$\frac{Until}{A}$his last class at the university in 1978, Hasan always $\frac{turns}{B}$ in all $\frac{of}{C}$ his assignments $\frac{on}{D}$ time.

Correct the sentence.

Which is the correct sentence?