13 Put the adjectives in brackets into the correct degree. At a physics lesson the teacher asked the children about the effect of heat and cold on the body. «Heat makes things (big) and cold makes things (small)», answered (bright) boy of the class. «Quite right», said the teacher. «Can you give us an example?» «In summer, when it is hot, the days are (long), but in winter, when it is cold, the days are ... (short)», answered .. the boy.

"In summer, when it is hot, the days are longer, but in winter, when it is cold, the days are shorter", answered the boy.

In this sentence, we need to put the adjectives in the correct degree. Let's analyze the adjectives in the brackets.

- The first adjective is "big". To compare the effect of heat on things, we need to use the comparative degree. So, it should be "bigger".

- The second adjective is "small". To compare the effect of cold on things, we also need to use the comparative degree. So, it should be "smaller".

- The third adjective is "bright". This adjective doesn't require any comparison, as it already describes a quality of the boy. So, it should remain the same.

- The fourth adjective is "long". To compare the length of the days in summer and winter, we need to use the comparative degree. So, it should be "longer".

- Finally, the fifth adjective is "short". Since we are comparing the length of the days in summer and winter, we need to use the comparative degree. So, it should be "shorter".

Putting it all together, the sentence should be: "In summer, when it is hot, the days are bigger, but in winter, when it is cold, the days are smaller", answered the brightest boy of the class.