सौर सेल (solar cells) में मुख्य रूप से निम्नलिखित में से किस तत्व का उपयोग किया जाता है?

The 'Drain of Wealth' theory was propounded by which Indian nationalist leader?

Which event is considered the turning point in Mahatma Gandhi's leadership in the Indian independence movement?

Which African leader is known for his non-violent opposition to colonial rule?