做的实验就写写类似相关实验的优劣吧），这部分注意写reference。
然后介绍一下实验过程。 如果实验用了一些非常见的仪器，也可以在这个部分做一个简要介绍。
再转一篇我认为写得很好的Introduction example
Introduction
In this lab, we explore the theory of optimal foraging and the theory of central place foraging using beavers as the model animal. Foraging refers to the mammalian behavior associated with searching for food. The optimal foraging theory assumes that animals feed in a way that maximizes their net rate of energy intake per unit time (Pyke et al. 1977). An animal may either maximize its daily energy intake (energy maximizer) or minimize the time spent feeding (time minimizer) in order to meet minimum
requirements. Herbivores commonly behave as energy maximizers (Belovsky 1986) and accomplish this maximizing behavior by choosing food that is of high quality and has low-search and low-handling time (Pyke et al. 1977).
The central place theory is used to describe animals that collect food and store it in a fixed location in their home range, the central place (Jenkins 1980). The factors associated with the optimal foraging theory also apply to the central place theory. The central place theory predicts that retrieval costs increase linearly with distance of the resource from the central place (Rockwood and Hubbell 1987). Central place feeders are very selective when choosing food that is far from the central place since they have to spend time and energy hauling it back to the storage site (Schoener 1979).
The main objective of this lab was to determine beaver (Castor canadensis) food selection based on tree species, size, and distance. Since beavers are energy maximizers (Jenkins 1980, Belovsky 1984) and central place feeders (McGinley and Whitam 1985), they make an excellent test animal for the optimal foraging theory. Beavers eat several kinds of herbaceous plants as well as the leaves, twigs, and bark of most species of woody plants that grow near water (Jenkins and Busher 1979). By examining the trees that are chewed or not-chewed in the beavers’ home range, an accurate assessment of food preferences among tree species may be gained (Jenkins 1975). The purpose of this lab was to learn about the optimal foraging theory. We wanted to know if beavers put the optimal foraging theory into action when selecting food.
We hypothesized that the beavers in this study will choose trees that are small in circumference and closest to the water. Since the energy yield of tree species may vary significantly, we also hypothesized that beavers will show a preference for some species of trees over others regardless of circumference size or distance from the central area. The optimal foraging theory and central place theory lead us to predict that beavers,