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  3. Like all animal species, plant species must spread their offspring to suitable areas where they can grow and pass on their paren

Like all animal species, plant species must spread their offspring to suitable areas where they can grow and pass on their paren

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问题    Like all animal species, plant species must spread their offspring to suitable areas where they
can grow and pass on their parent’s genes.
Young animals generally spread by walking or flying.                       【M1】_____
Because plants don’t have that ability,
they may somehow hitchhike. Some plant seeds scatter by                   【M2】_____
blowing in the wind or floating on water. Many other plant species, though, trick an animal into
carrying their seeds. How do they do? They enclose them within a tasty fruit and advertise the fruit’s
ripeness by its color or smell.
The hungry animal collects and swallows the fruit, walks or flies off, but 【M3】_____
later spits out the seeds somewhere far from its parent tree.
Seeds can thereby be carried thousands                                     【M4】_____
of miles. It may surprise you to learn that plant seeds can resist digestion. In fact, some seeds
actually require passage through an animal’s body before they can grow. Wild strawberries offer a
good example of hitchhiking tactic.
When strawberry seeds are still young and not yet ready to be              【M5】_____
planted, the surrounding fruit is green, sour, and hard.
When the seeds final mature, the berries turn                              【M6】_____
red, sweet, and tender. The change in the berries’ color serves as a signal to birds which then eat the strawberries, fly off, and eventually spit out the seeds.
Naturally, strawberry plants doesn’t set out                               【M7】_____
with a conscious intent of attracting birds only when
their seeds were ready to be dispersed away.                               【M8】_____
Nor did birds set out with the intent of planting strawberries. Rather, strawberry plants evolved
through natural selection.
The sweeter and reder the final strawberry, the more birds spread its ripe 【M9】_____
seeds;the greener and more sour the young strawberry,
the birds destroyed the seeds by eating                                     【M10】_____
berries before the seeds were ready.
【M2】
选项
答案may改成must
解析 情态动词语气不同，must强调必须，不得不，只能。
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