Questions

a) joins the Gulf of Mexico and Atlantic Ocean, and touches USA and Bahama Island.

b) joins the sea of Marmara and Aegean Sea, touching Asian Turckey and European  Turkey

d) joins Black sea and sea of Marmara touching Asian Turkey and European Turkey

The given sentence is in simple present tense and states a general fact, hence the latter half of the sentence with the blank will also be in the simple present tense. Since the subject in the latter part of the sentence is singular .i.e. 'the number', the verb will be followed accordingly. Hence, option 4 is the correct answer.

Centrifugal force is the fictitious force that pulls out from the center on the body we feel while moving in the circular path. It increases with the rate of rotation of the axis i.e, acceleration of the body.