一种植物通过分泌次生代谢物，对其他植物或微生物产生影响的现象叫______。

Teachers need to be aware of the emotional, intellectual, and physical changes that young adults experience. And they also need to give serious (51) to how they can be best accommodate such changes. Growing bodies need movement and (52) , but not just in ways that emphasize competition. Because they are adjusting to their new bodies and a whole host of new intellectual and emotional challenges, teenagers are especially self-conscious and need the (53) that comes from achieving success and knowing that their accomplishments are admired by others. However, the typical teenage lifestyle is already filled with so much competition that it would be (54) to plan activities in which there are more winners than losers, for example, publishing newsletters with many student-written book reviews, (55) student artwork, and sponsoring book discussion clubs. A variety of small clubs can provide multiple opportunities for leadership, as well as for practice in successful (56) dynamics. Making friends is extremely important to teenagers, and many shy students need the (57) of some kind of organization with a supportive adult (58) visible in the background.

In these activities, it is important to remember that the young teens have (59) attention spans. A variety of activities should be organized (60) participants can remain active as long as they want and then go on to something else without feeling guilty and without letting the other participants down.

54().

A.improper 

B.risky 

C.fair 

D.wise