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

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.

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?

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?