mits of a person’s intelligence, generallyspeaking ,are fixed at birth, but hereaches these limits will depend on his environment

下列各句中，没有语病的一句是( )

Most birds find it safe to sleep in the trees, but __________ they have eggs or young chicks, they don’t use a nest.

Mr. Black________ Shanghai in a few days. Do you know when the earliest plane ________on Sunday

It was _____________ back home after the experiment.