问中学，
真会学。

Light travels far faster than sound

提示Both set off together from one place, so compare how quickly each makes the trip.

为什么The flash and the bang are made at the same instant. The flash reaches you almost immediately, while the thunder crosses the air at about 340 metres every second, so it lags further behind the further away the storm is.

Potatoes reached Europe from the Americas long after Roman times

提示Think about which continent the vegetable was first grown in.

为什么Potatoes came to Europe in the 1500s after contact with the Americas, around a thousand years after the Romans left Britain.

Helium is unreactive and will not burn, whereas hydrogen can catch fire or explode

提示Think about what could happen near a flame.

为什么Both gases are lighter than air, but hydrogen burns explosively. Helium belongs to the noble gases, which hardly react at all, so it is safe.

Two

提示It is the smallest prime of all, and it divides into every single even number you can name.

为什么A prime has exactly two factors: itself and 1. Two qualifies, because its factors are 1 and 2. One does not, since it has only a single factor — which is why 1 is never counted as a prime.

A cold is caused by a virus; antibiotics kill bacteria

提示These medicines target just one group of microbes, and that group is not what gives you a runny nose.

为什么Antibiotics attack structures that only one group of microbes has, such as the cell wall. Taking them for a viral illness does nothing and helps resistant strains spread.