英语改错I came to understand that was not easy to lean moneyWhen

I came to understand that it was not easy to earn money
When he bought a chocolate cake,he put it in a secret place
The truck was moving so fast that the driver couldn't control it
We must take part in the social practice to prepare ourselves well for our future
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I came to understand that was not easy to 【earn】 money
When he bought a chocolate cake,he put 【it】 in a secret place
The truck was moving so fast that the driver couldn't control 【it】
We must take part in【/】social practice to prepare us well for our future