根据以下资料回答第39、40题。
 For people, and many other animals, family matters. Consider how many jobs go to relatives.Or how an ant will cruelly attack intruder ants but rescue injured, closely related nest-mates. Thereare good evolutionary reasons to aid relatives, after all. Now, it seems, family feelings may stir inplants as well.
A Canadian biologist planted the seed of the idea more than a decade ago, but many plantbiologists regarded it as heretical ( 异端的 ,旁门左道 的) --plants lack the nervous systems thatenable animals to recognize kin, so how can they know their relatives? But with a series of recentfindings, the notion that plants really do care for their most genetically close peers--in a quiet,plant way--is taking root. Some species constrain how far their roots spread, others change howmany flowers they produce, and a few tilt or shift their leaves to minimize shading of neighboringplants, favoring related individuals. 
"We need to recognize that plants not only sense whether it's light or dark or if they've beentouched, but also whom they are interacting with," says Susan Dudley, a plant evolutionaryecologist at McMaster University in Hamilton, Canada, whose early plant kin recognition studiessparked the interest of many scientists. 
Beyond broadening views of plant behavior, the new work may have a practical side. InSeptember 2018, a team in China reported that rice planted with kin grows better, a finding thatsuggested family ties can be exploited to improve crop yields. "It seems anytime anyone looks forit, they find a kin effect," says Andr6 Kessler, a chemical ecologist at Comell University.
What may be the plants' way of expressing their care for relatives?