我不明白的句子们(tpo)

◆Forehead rubbing by male deer on buck rubs presumably sends a great deal of information to other members of the same species. First, the chemicals deposited on the rub provide information on the individual identity of an animal; no two mammals produce the same scent. For instance, as we all know, dogs recognize each other via smell. Second, because only male deer rub, the buck rub and its associated chemicals indicate the sex of the deer producing the rub. Third, older, more dominant bucks produce more buck rubs and probably deposit more glandular secretions on a given rub. Thus, the presence of many well-marked rubs is indicative of older, higher-status males being in the general vicinity rather than simply being a crude measure of relative deer abundance in a given area. The information conveyed by the olfactory(嗅觉的) signals on a buck rub make it the social equivalent of some auditory （听觉的）signals in other deer species, such as trumpeting by bull elk.

◆As recently as 6000 B.C, the southern frontier or the desert was far to the north of where it is now, while semiarid（半干旱）grassland and shallow freshwater lakes covered much of what are now arid plains.

◆In 1820 under a new land law, a farm could be bought for USD100. The continued proliferation of banks made it easier for those without cash to negotiate loans in paper money. Western farmers borrowed with the confident expectation that the exploding economy would keep farm prices high, thus making it easy to repay loans when they fell due.

◆If so, the green algae would have been subjected to environmental pressures that resulted in adaptations that enhanced their potential to give rise to land-dwelling or organisms.

◆These include conducting vessels that transport water and minerals upward from the roots and that move the photosynthetic products from the leaves to the rest of the plant body and the stiffening substance lignin, which support the plant body, helping it expose maximum surface area to sunlight.

◆Protected embryos and waterless dispersal of sex cells were achieved with the origin of seed plans and the key evolutionary innovations that they introduced: pollen, seeds, and later, flowers and fruits.

◆For years historians have sought to identify crucial elements in the eighteenth-century rise in industry, Known as the Industrial Revolution, and many give

26-1-1）多年来，历史学家试图找到18世纪工业革命在工业、技术和经济领域兴起的关键因素，许多人把能源问题放在突出位置。

◆The availability of steam power and the demands for new machines facilitated the transformation of the iron industry. Charcoal, made from wood and thus in limited supply, was replaced with coal-derived coke (substance left after coal is heated) as steam-driven bellows came into use for producing of raw iron. 26-1-3蒸汽动力的可利用性以及对新机器的需求促进了钢铁工业的转型。当蒸汽驱动风箱投入到生铁生产中后，木炭这种用木材烧成因此供应量有限的物质就被焦炭（煤加热后残留的物质）替代了。