Glands of the endocrine system release their hormones a) directly onto the hormones' target cells b) directly onto the skin's epithelial cells c) into the bloodstream d) into attached ducts

C) into the bloodstream

Explanation:

The endocrine gland system release their hormones into the bloodstream rather then in the ducts. This facilitates the transport of the hormones to the other parts of the body and perform the action role in those parts. The glands of the endocrine system includes the pineal gland, pancreas, ovaries, thyroid gland, adrenal glands, parathyroid gland, hypothalamus and pituitary gland.  

The hormones secreted by these glands help in controlling the growth, development, reproduction and metabolism.

before, trains worked using the steam engine. thus, it uses heat so it is crucial to apply heat balance. the steam engine absorbs energy during the stage of boiling water. so, this is the endothermic reaction. when the steam is used to work the piston, it has to release this energy through running the train. the excess energy is released as an exhaust to the chimney. this is the exothermic process because it releases energy to the surroundings.