When performing heart surgery, a physician would use to make an incision and to hold tissues back so the surgeon can reach the heart.
a. forceps, a tenaculum
b. hemostats, a speculum
c. a scalpel, retractors
d. a probe, a towel clamp

That's pretty easy, I am absulutely sure that the tools from the third option of the scale attached above best suit the gaps from the passage which you represented. So, the right answer is c. a scalpel, retractors

The passage should look like this : 
When performing heart surgery, a physician would use scapel to make an incision and retractors to hold tissues back so the surgeon can reach the heart.

The correct answer would be option C. A scalpel and retractors. When performing heart surgery, a physician would use a scalpel to make an incision and retractors to hold tissues back so the surgeon can reach the heart. A scalpel is a small knife with a detachable blade used by surgeons during surgery. A retractor is a surgical instrument used by surgeons to hold back underlying tissues and organs.

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Explanation:

it is 100 sheets of paper divide 0.5 by 100 to get the estimated length of a single sheet