（10）The problem of stress gets worse when people keep their worries to{#blank#}10{#/blank#} (they).
（11）My mother is far too busy{#blank#}11{#/blank#} (do) housework.
（12）To tell you the {#blank#}12{#/blank#} (true), I often quarrel with my parents.
（13）My classmate, Jack, has just found a book {#blank#}13{#/blank#} (lie) on the playground.
（14）In fact, many teenagers have no {#blank#}14{#/blank#} (communicate) with family members.
（15） I think you can talk to your friends when{#blank#}15{#/blank#} (feel) sad.

It's hard for a girl to doing research on the wild animals for three years.