Read the text. Then, answer the questions!

    Mass production involves making many copies of products, very quickly, using line techniques to send partially complete products to workers who each work on an individual step, rather than having a worker work on a whole product from start to finish.

    Mass production of fluid matter typically involves pipes with centrifugal pumps or screw conveyors (augers) to transfer raw materials or partially complete product between vessel.  Fluid flow processes such as oil refining and bulk materials such as wood chips and pulp are automated using a system of process control which uses various instruments to measure variables such as temperature, pressure, volumetric and level, providing feedback.

    Bulk materials such as coal, ores, grains and wood chips are handled by belt, chain, slat, pneumatic or screw conveyors, bucket elevators and mobile equipment such as front-end loaders. Materials on pallets are handled with forklifts. Also used for handling hear, like reels of paper, steel or machinery are electric overhead cranes, sometimes called cranes because they span large factory bays.

    Mass production is capital intensive and energy intensive, as it uses a high of machinery and energy in relation to workers. It is also usually automated while total expenditure per unit of product is decreased. However, the machinery that is needed up a mass production line (such as robots and machine presses) is so expensive that there must be some assurance that the product is to be successful to attain profits.

(Source: http://en.wikipedia.org/wiki/Mass_production

What is special about the passive sentences?