The correct options are
A Global warming
C Pollution
During continuous rainfall, a large amount of water is received in a particular region. Flood occurs when such large amount of water cannot be drained into ground or other waterbodies.
The release of harmful gases like carbon monoxide into the atmosphere leads to a rise in the temperature of the Earth. This gradual rise in the Earth's temperature is known as global warming. It can lead to the melting of polar ice caps and consequently cause flood.
However, drip irrigation and rainwater harvesting are water conservation techniques.