Which is the best method to obtain virus-free plants through tissue culture?

$A$ column of water within xylem vessels of tall trees does not break under its weight because of

Suppose $E$ and $F$ are two events of a random experiment. If the probability of occurrence of $E$ is $1/5$ and the probability of occurrence of $F$ given $E$ is $1/10$,then the probability of non-occurrence of at least one of the events $E$ and $F$ is

$A$ transistor having a $\beta$ equal to $80$ has a change in base current of $250 \mu A$. The change in collector current is:

The angle between the tangents drawn to the parabola $y^2=4x$ from the point $(1,4)$ is

The position of a particle at time $t$ is given by the equation $x(t) = \frac{v_0}{A}(1 - e^{-At})$,where $v_0$ is a constant and $A > 0$. The dimensions of $v_0$ and $A$ respectively are: