Astudent who grew up in a tropical country and is studying in the united states may have no experience with static electricity sparcs and shocks until his or her first american winter. why is that so?

Since tropical countries have humid air, which is full of water vapor, it neutralizes charge and electricity, so it is usually impossible to experience static electricity sparks and shocks because it is always hot.
In America, however, especially during winter months, it is obviously not as hot, so the air is not humid, thus these sparks and shocks can be created. 

Australian English was influenced by the language of the indigenous people originally in Australia before colonisation. Over the next 80 years, Australia was the destination for many convict ships with the last one reaching Western Australia in 1868