Answer :
What Bob can conclude after 4 days when the seedlings emerged from the soil is that;
The seedlings exerted an upward pushing force on the soil.
Since he planted some seeds in a cup of soil and puts water and light daily into it, it means that the seedling is supposed to germinate and begin to grow.
However, we are told that after 4 days, the seedlings emerged from the soil. What this means is that the seedlings didn't germinate and as such they instead forced their way up the soil with an upward pushing force.
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