When nests during spring nesting season, Canadian geese are fiercely territorial.
When _____________ nests during spring nesting season, Canadian geese are fiercely territorial.
A. building
B. are building
C. built
D. are built
Đáp án A
Dịch nghĩa: Khi xây tổ trong suốt mùa xuân, ngỗng Canada "phân chia địa bàn" quyết liệt.