Two studies were carried out to determine if children in daycare got more ear infections than children who stayed at home. The first study compared ear infection rates in 50 Canadian girls ages 1 to 2, half of whom attended daycare and half of whom stayed home. The second study compared ear infection rates in 1000 Swedish boys ages 3 to 4, half of whom attended daycare and half of whom stayed home. The results of these two studies differed greatly. Which of the following is LEAST likely to be the cause of such differences?

The periodic table displays the elements arranged according to

If you were to dissect a plant into smaller and smaller units, what is the smallest unit that would still be considered alive?

Which of the following types of chemical bonds involves the sharing of electrons?

A(n)  _____  is a charged atom.

A polar covalent bond is formed by

You have the following known facts: Smoking causes accumulation of materials in the lungs, thereby decreasing oxygen-absorbing capability of the lungs. Long-term smoking causes more accumulation of materials in the lungs. Decreased lung capacity increases the workload of the heart. Which of the following hypotheses can you make from these observations?

Studies described in the textbook involving coffee drinking have shown evidence for all of the following EXCEPT

I notice that all the students in my class seem very drowsy 45 minutes into my class period. Knowing that it could not possibly be my lecture putting them to sleep, I consider other factors such as the fact that my class is at 5 p.m. and the sun is usually setting at that time of the day, which I think may make people drowsy. What type of evidence am I collecting in making this observation?

Which of the following substances has the lowest pH?