Explanation

She had been studying for three hours when the power went out.

"Had been studying" is a past perfect continuous tense.

It indicates an action that began in the past.

The action continued for a duration of time.

It ended before another past event (when the power went out).

Explanation

She wants to buy a car is the sentence that uses the article correctly.

"A" is used before singular, non-specific nouns that begin with a consonant sound.

Explanation

The sentence should be: "If he had studied harder, he would have passed the exam."

This is a third conditional sentence used for hypothetical situations in the past.

Explanation

The cellphone was invented on April 3, 1973, by Dr. Martin Cooper at Motorola.

He made the first mobile phone call.

This marking a significant milestone in communication technology.

Explanation

He doesn't like broccoli is the grammatically correct sentence.

The contraction "doesn't" is used with the base form of the verb "like".

Explanation

Radio waves are used for sending sound waves over large distances.

They are capable of transmitting signals over long ranges.

This making them ideal for communication systems like radio and television.

Explanation

Sound travels faster in iron than in air.

This is because sound waves move more quickly through denser materials.

Like iron, compared to less dense ones, like air.

Explanation

The original name of the host of the Holy Prophet Muhammad (PBUH) was Khalid bin Zaid (R.A).

He is better known as Abu Ayub Ansari (R.A).

He provided refuge to the Prophet during his migration to Madinah.