Springs (hot springs) and geysers are formed when the water from the interior of the earth are ejected into the earth's surface. In simple words, these are formed in the region where the groundwater and the ground surface intersects with each other.
The water obtained from springs can be cold or hot. Those that produce hot water are termed as hot-spring. These hot springs and geysers indicates the occurrence of volcanic activity. This water becomes hot due to the interaction with the magma at certain depths below the ground surface.
The geysers are also a type of hot-springs which produces hot water.
Excitation-contraction coupling refers to the series of events that begins with the excitation of the sarcolemma in response to stimulation by a neurotransmitter, and results in the release of calcium ions from the sarcoplasmic reticulum.
Hence, option D is the 1st process that starts the excitation-contraction coupling.
