Length = 120ft
Breadth = 80ft
$$Total\ area=120\cdot80=9600ft^2$$
If partitioned into 10 rectangular gardens, then area of each rectangular garden = 9600/10 = 960 ft^2.

So, the questor bothers on how many feet of partitioning will be needed to separate the garden.
Statement 1: One of the dimensions of each garden is to be 40ft.
And, Area = length * Breadth
$$960=length\cdot40$$ $$l=\frac{960}{40}=24ft$$
$$l=\frac{960}{40}=24ft$$
Hence, we have 40ft * 24ft rectangules. The 24 ft will fill the 120 ft 5 times and the 40ft in 80ft direction will go 2 times. So, the 10 rectangular gardens will be 2*5 or 5*2.
Partition to separate each garden = Perimeter of each garden = l+b
= 40 + 24 = 64ft.
Therefore, 64ft partition is needed to separate the garden. Hence, statement 1 is SUFFICIENT.

Statement 2: One of each dimension of each garden is to be 24 ft.
Area = length * Breadth
$$960=24\cdot breadth$$
$$b=\frac{960}{24}=40ft$$
Hence, we have 40ft *24ft rectangules. This is the same as statement 1, so therefore, statement 2 is also SUFFICIENT.

Conclusively, each statement alone is SUFFICIENT. Thus, the correct answer is Option D.

Thanks