Explanation-1

If you do not glue them properly, it leads to the collapse of the tower.

A) No change

B) may lead

C) led

D) will have led

Explanation-2

Mark slept the entire day; his friend felt that the entire day had been wasted by him.

A) No change

B) he was wasting the entire day

C) the entire day will have been wasted by him

D) he had wasted the entire day

Explanation-3

Though doing pilates is usually a hobby, Tina felt therapeutic particularly on stressful days it was.

A) No change

B) Tina felt, on particularly stressful days, that it was actually therapeutic

C) Tina felt therapeutic, particularly on stressful days.

D) Tina having felt, in particularly stressful days, that it actually seems therapeutic.

Explanation-4

If you were an Elsa, then I would be Elf.

A) No change

B) was

C) is

D) are

Explanation-5

It is imperative that the Dean are present at the addressing ceremony tonight.

A) No change

B) was

C) be

D) being