Fill in the Blanks

Village is an enclosed region, hence 'in' is used.

Whenever we want to show the complete time taken to accomplish a task, we use 'in' for the time period.

Mitochondria are tiny structures that occur in varying shapes cylindrical, spherical, oval, rod shaped etc.. They are found distributed all over the cytoplasm. Each mitochondrion is bound by a double membrane. The outer membrane is smooth and straight, while the inner membrane is thrown into numerous folds called cristae. Thus, the surface area of inner membrane is much higher than that of outer membrane. The cristae bear numerous, minute, regularly spaced particles called elementary particles or oxysomes.

A ribosome is a component of a biological cell that creates proteins from all amino acids and rRNA representing the protein. Ribosomes are made from complexes of rRNAs and proteins. Ribosomes are divided into two subunits. The smaller subunit binds to the mRNA, while the larger subunit binds to the tRNA and the amino acids.

The centrosome is an organelle that serves as the main microtubule organizing center (MTOC) of the animal cell as well as a regulator of cell-cycle progression. It was discovered by Edouard Van Beneden in 1883. The centrosome is thought to have evolved only in the metazoan lineage of eukaryotic cells.Doubling of a centrosome is similar to the DNA replication in two respects: the semi-conservative nature of the process and the action of cdk2 as a regulator of the process.

For referring to specific point of time, we use 'at'. 

Action is performed 'by' people 'with' instruments.

To refer to a specific point of time of past, we use 'since'.

The sentence implies that 'nobody except you knows the truth'. 'But' means the same as 'except'.

'Besides rice' means 'apart from rice'.

To refer to specific time in the past, we use the preposition 'since'.

'Jumped at' means 'accepted at once'. This meaning fits in the framework of the meaning of the sentence.

'Kept in' means 'restrained'. This meaning fits in the framework of the meaning of the sentence.

'Knocking about' means 'loitering aimlessly'. This meaning fits in the framework of the meaning of the sentence.

'Led on' means 'enticed'. This meaning fits in the framework of the meaning of the sentence.