Answer:
D. 7°C
Explanation:
The difference between two numbers is the distance between them on the number line.
4 -(-3) = 4 +3 = 7
Temperatures -3°C and +4°C are 7°C apart. The difference between the temperatures is 7°C.
_____
Additional comment
Often, in math, when we talk about the difference between A and B, we mean specifically the value (A-B). In plain English, when we talk about the difference between A and B, we mean the positive difference--the value obtained by subtracting the smaller number from the larger one.
Here, the difference between New York and London temperatures would ordinarily be interpreted in math to be -3 -4 = -7°C. That is not an answer choice, so we must assume the positive difference, 7°C, is intended.