191.

Study the following statements

1. Chromosomes are located in the nucleolus.
2. Genes are located in the chromosomes.
3. Unicellular organisms respire and reproduce.
4. The most important function of the cell membrane is to control the entry and exit of materials from cells.

The correct statements are

• A, C and D

• A, B and D

• A, B and C

• B, C and D

The ultrasound equipments used for investigating medical problems work at frequency

• between 2000 Hz and 20000 Hz

• above 20000 Hz

• below 20 Hz

• between 20 Hz and 200000 Hz