Question 18 asks for the English translation of the French idiom "Avoir le cœur sur la main".

Question 18 asks for the English translation of the French idiom "Avoir le cœur sur la main".

The French idiom "avoir le cœur sur la main" means to be generous, kind, and open-hearted.

Let's examine the given options:
A. "To have the heart on the hand" is a literal translation, but not the idiomatic equivalent in English.
B. "To have a heart of gold" is an English idiom that means to be very kind and generous. This perfectly matches the meaning of the French idiom.
C. "To be very weak" is incorrect.
D. "To be very strong" is incorrect.

Therefore, the correct translation is "To have a heart of gold".

The final answer is $\boxed{\text{B}}$