A relatively small blood pressure gradient is generally insufficient to move blood through the veins under given conditions, thus venous return must be facilitated by valves within veins and two "pumps." ... As skeletal muscles contract, veins are squeezed to help propel the blood toward the heart.
The answer is surely D cuz I've done this question in a test before. Hoped I helped ;)
Answer:
Renewable energy: solar radiation
Farm example: Farm located in Heggelbach, Germany
Explanation:
Solar radiation is one of the most used types of renewable energy. It proportionates light during the whole day (even during the cloudy days), which is received by solar photovoltaic panels. These photovoltaic panels are formed by solar cells that turn the solar light (photons) into electricity (electrons) through the photoelectrical process. Certain materials are capable of absorbing photons and releasing electrons, generating by this movement, electric current.
Solar energy is being used in many places to avoid using fossil fuels as energy sources and replace them. Specifically, in farms, this energy is used for equipment operation and machinery use.
Even the combination of solar panels and agriculture is taking place in the same land area or parcel. In the same place where solar panels are installed, and under them, vegetables are being grown. The advantage for certain vegetable species is that panels protect from excessive radiation or other adverse climatic conditions.
<u>Example:</u>
In 2018 in Heggelbach - Germany- a five meters structure of solar panels was installed on a farm. Under them, different crops were grown. The production under the photovoltaic system was highly superior to the traditional one. The efficiency of land use increased by 186% per hectare with the agro-photovoltaic system.
