In order to produce electricity using tidal power the difference between high and low tides must be at least meters.
a) 2
b) 3
c) 4
d) 5

d) 5 m

Explanation:

Barrages could be built on the ebb side, or flood side, or even both, to produce electricity. Tidal height can vary from location to location over a broad range (4.5-12.4 m). For profitable operations and adequate water head for the turbines, a tidal range of at minimum 7 m is needed.

So, the appropriate option for the given situation is d.

find the surface area of the sphere to the nearest square unit. use a calculator.

a. 254 in.2

b. 64 in.2

c. 127 in.2

d. 1,018 in.2

it is given that trillions of microbes make up to 1% to 3% of the body mass.

let's take average of this percentage: 2%

consider the average mass of the human body as 70 kg.

then, trillions of microbes would have mass  

therefore, 100 trillion micro-organisms would weigh:

this is an approximate value and could change depending on the mass of the human body and percentage of the microbes present in it.

average mass per microorganism =